Duration Of Lactational Amenorrhea Research Articles

CORRELATION BETWEEN EXCLUSIVE BREASTFEEDING IN GROUP OF EARLY INITIATION OF BREASTFEEDING ON THE DURATION OF LACTATIONAL AMENORRHEA

Introduction: Based on data from "Survei Demografi dan Kesehatan Indonesia" (SDKI) in 2012, about four percent of births occurred 18 months apart, and six percent were less than two years apart, about 75 percent occurred at least three years apart. WHO’s recommendation for birth spacing is at least 24 months. A gestation interval of fewer than six months can increase maternal mortality due to premature rupture of the amniotic sac, anemia, and puerperal endometritis. The Lactational Amenorrhea Method is a natural and easy method of contraception. The LAM method is one of the contraceptive methods with a success rate of 98 percent. One of the importance of contraception, such as LAM, is to adjust the optimal birth spacing. Purpose: This study aims to determine the correlation between exclusive breastfeeding in a group of early initiation of breastfeeding on the duration of lactational amenorrhea. Method: This study is an observational analytic study with a retrospective cohort study design. A simple random sampling technique is used for the sampling method. The collection of data on the history of breastfeeding and the duration of amenorrhea was collected from the main research results by doing interviews with respondents. Results: The results of statistical tests with Spearman correlation showed that the P-value obtained is 0.005. This value is less than p (0.05), which means a significant correlation between exclusive breastfeeding and the duration of lactational amenorrhea. Conclusion: There is a significant correlation between exclusive breastfeeding in the early initiation of the breastfeeding group and the duration of lactation amenorrhea.

Progesterone vaginal ring as a new contraceptive option for lactating mothers: Evidence from a multicenter non-randomized comparative clinical trial in India

ObjectivesEvaluate and compare contraceptive efficacy, safety, continuation rates and duration of lactational amenorrhea (LA) in married lactating women (20–35 years) using the progesterone vaginal ring (PVR) or Copper-T380A intrauterine device (IUD) during the first postpartum year. Study designWe conducted a one-year multicenter, non-randomized, non-inferiority, open-label, comparative trial at 20 centers in India and compared efficacy, safety, continuation and LA plus feeding patterns and growth/well-being of participants’ infants. Women used four 3-month PVRs consecutively (lost PVRs were not replaced) and were to breastfeed at least four times/day. We used Pearl Index (PI) and Kaplan Meier (K-M) rates to analyze pregnancy and K-M for continuation. ResultsWe enrolled 789 women (459 PVR, 330 IUD). Neither PI nor K-M one-year pregnancy rates differed significantly between groups (PI: PVR-0.62; IUD-0.35); (K-M: PVR-0.7; IUD-0.4, p = 0.58). Continuation rates at 12 months were 78.5% (IUD) vs. 56.9% (PVR) (p < 0.001). Ring expulsions and menorrhagia were the most common discontinuation among PVR/IUD users respectively. The median duration of LA among PVR vs. IUD users was 405 vs. 120 days (p < 0.001). Both groups reported similar adverse events (PVR: 24.2%; IUD: 23.0%); there were no serious adverse events among PVR users. Infants from both groups fed 12–7 times/day and grew at expected rates. ConclusionsEfficacy and safety outcomes were comparable among women in both groups. Continuation rates for PVR, a woman-controlled method, were shorter than IUD rates while PVR users maintained LA significantly longer than IUD users. Infant breastfeeding and growth patterns/well-being were favorable in both groups. ImplicationsPVR, a user-controlled device, offers an additional contraceptive choice for lactating women for one-year postpartum use and can help to address the unmet need for contraception among postpartum women while encouraging breastfeeding to enhance infant growth and well-being.

Risk of Pregnancy in Breastfeeding Mothers: Role of the Progesterone Vaginal Ring on Birth Spacing

The progesterone vaginal ring (PVR) Progering® has been shown to be effective as a contraceptive in breastfeeding women who need safe and effective methods of spacing pregnancies. Previous clinical trials, of 1-year duration, demonstrated its efficacy to be similar to that of the intra-uterine device (IUD) during lactation. The duration of lactational amenorrhoea is significantly prolonged in PVR users in comparison with IUD users with fewer median numbers of bleeding/spotting episodes and days. This delivery system designed for 3-month use needs to be renewed every 3 months as long as breastfeeding continues, for up to 1 year. The frequency of breastfeeding, breast milk volume, and infant growth were not different in PVR or IUD users, and the safety of this new method has been well documented. This article reviews the literature and describes the mechanism of action of the PVR during lactation to bring additional protection over exclusive breastfeeding only, during the first year postpartum. Further evaluation of the PVR acceptability in different populations where breastfeeding is popular and highly recommended for the infant’s benefit is warranted.

Lactation, maternal nutrition and fertility.

Due to the fact that the duration of postpartum infertility varies widely among lactating women, breastfeeding is considered to be an unreliable contraceptive method. At this time there is no simple or reliable procedure to detect when fertility returns. Consequently, lactating women are usually advised to use artificial forms of contraception. Yet, breastfeeding does have a considerable demographic impact. In the Philippines and Bangladesh, breastfeeding has been found to be more effective as a fertility control measure than oral contraceptives (OCs). In some countries the birth spacing effect of lactation is reinforced and safeguarded by the traditional custom of postpartum sexual abstinence. Maternal-based prolactin concentrations remain elevated for longer when infants are permitted to breastfeed on demand, and differences in the frequency and vigor of sucking are believed to be responsible for much of the variation in the duration of postpartum infertility. Although maternal nutritional status has been suggested as an influencing factor, no firm conclusion has been possible because of the presence of confounding variables which affect the duration of lactation or the frequency of suckling, such as differences in socioeconomic status or the provision of supplementary weaning foods. To exclude these variables, Prema et al. investigated nutrition-fertility interactions in a homogenous, low income group of 2250 Indian women who had never used any form of contraception and who lived in an area where there were no nutritional or health interventions. There were 2042 mothers in the study who breastfed their infants, and the duration of exclusive breastfeeding averaged 8.9 months; the total duration of lactation averaged 20.7 months. The mean duration of postpartum amenorrhea was 11.2 months and of interpregnancy interval was 24.2 months. For the 286mothers who did not breastfeed the mean duration of postpartum amenorrhea was only 4.6 months and the mean interpregnancy interval was 17.3 months. To assess the effect of maternal nutrition on fertility, the women were divided into 5 groups on the basis of body weight. The mean duration of exclusive breastfeeding, total duration of lactation, and duration of postpartum amenorrhea were all significantly shorter in women with body weight above 55 kg. When total duration of lactation was kept constant, there was a progressive fall in the duration of lactational amenorrhea with increasing body weight. If the conclusion that malnutrition reduces fertility is accurate, it is important to be aware that efforts to improve the diets of lactating women in the 3rd world may shorten birth intervals and exacerbate an already serious population growth problem.

Breast-Feeding and Lactational Amenorrhea in the United Arab Emirates

This study was designed to investigate the relation of breast-feeding and weaning practices with the duration of lactational amenorrhea among breast-feeding mothers in the United Arab Emirates. A total of 593 mothers were interviewed in the Maternal and Child Health Centers in three areas: Abu Dhabi, Dubai, and Al Ain. The total mean duration of lactational amenorrhea in this study was 6.1 months, and there was a direct relation with the length of exclusive breast-feeding. The duration of postpartum amenorrhea was the longest in Al Ain (7.2 months), as compared with Dubai (6.9 months) and Abu Dhabi (4.3 months). The age of the infant when formula milk and solid supplements were introduced was significantly related to the duration of lactational amenorrhea. This study confirms the results of other studies concerning the effectiveness of the lactational amenorrhea method as a natural method of contraception for the first 6 months postpartum, especially for mothers who breast-feed exclusively and more frequently and who delay the introduction of food supplements.

¿Son los niveles de prolactina y estradiol al tercer mes posparto factores predictores del tiempo de aparición de la primera menstruación posparto?: Modelo predictivo mediante análisis de sobrevida

The variability in the duration of lactational amenorrhoea (LA) lead to develop statistical multivariate models to predict the risk of the appearance of the first postpartum menstruation. To estimate the probability of recovering the first postpartum menstruation by means of a survival analysis, including hormonal levels and other parameters as predictor variables. Eighty one mothers in exclusive breastfeeding until the sixth postpartum month, in whom estradiol, basal and post suckling prolactin were measured at the third post partum month, were studied. The variables that better predict the appearance of the first menstruation between the 3rd and 12th postpartum months, were identified using a Cox model survival analysis. The median amenorrhea survival time (the lapse when the chance of recovering menstruation is 50%) was 209 days from delivery. Dichotomized estradiol and post suckling prolactin were the only significant variables that predicted the return of menstruation, with cutoff points of 190 pmol/ and 2,550 mIU/L, respectively. Post suckling prolantin and estradiol levels, measured at the third post partum month, are predictors for the time of appearance of the first postpartum menstruation.

Breast-feeding pattern and onset of menstruation among Yoruba mothers of South-west Nigeria

Objective To determine the breast-feeding practices and duration of lactational amenorrhoea among women within the first year of delivery in a Nigerian population.Method Cross-sectional study carried out between January 2005 and April 2006, among mothers within one year of delivery, who were attending the Infant Welfare Clinic at Wesley Guild Hospital, Ilesa, Nigeria. Using a semi-structured questionnaire, mothers were interviewed to obtain information regarding their socio-demographic characteristics, parity, breast-feeding habits, use of contraception and onset of menstruation after delivery. Information obtained was analysed using the Statistical Package for Social Sciences (SPSS) software version 11.Results All 268 (100%) mothers interviewed breast-fed their babies, 261 (97.4%) of which for at least 6 months. Most (71.6%) suckled exclusively for 6 months and more; only 10 (3.7%) never carried out exclusive breast-feeding. Age, parity and educational level did not affect the duration of exclusive breast-feeding. Lactational amenorrhoea lasted 3 months or more in 229 (85.5%) of the mothers. Of the 174 who exclusively breast-fed for 6 months, 109 (62.6%) remained amenorrhoeic during that time and, hence, met the criteria for use of LAM contraception.Conclusion Exclusive breast-feeding among nursing mothers is highly prevalent among Yoruba mothers of South-west Nigeria. Since lactational amenorrhoea lasts 6 months in about two-thirds of the women nursing for that period of time, there is a great potential for the application of LAM for contraception.

Lactational amenorrhoea in well-nourished Toba women of Formosa, Argentina.

The proximate causes of the contraceptive effect of lactation are still a matter of productive debate. This study sought to disentangle the relative impact that intense breast-feeding practices and maternal nutrition have on the regulation of ovarian function in nursing women. A mixed-longitudinal, direct-observational, prospective study was conducted of the return to postpartum fecundity in 113 breast-feeding, well-nourished Toba women. A sub-sample of 70 women provided data on nursing behaviour, daily activities, diet quality and urinary levels of oestrone and progesterone metabolites. Well-nourished, intensively breast-feeding Toba women experienced a relatively short period of lactational amenorrhoea (10.2 +/- 4.3 months) and a high lifetime fertility (TFR=6.7 live births/woman). Duration of lactational amenorrhoea was not correlated with any of the nursing parameters under study or with static measures of maternal nutritional status. The results indicated that the pattern of resumption of postpartum fertility could be explained, at least partly, by differences in individual metabolic budgets. Toba women resumed postpartum ovulation after a period of sustained positive energy balance. As the relative metabolic load hypothesis suggests, the variable effect of lactation on postpartum fertility may not depend on the intensity of nursing per se but rather on the energetic stress that lactation represents for the individual mother.

The optimal duration of exclusive breastfeeding: a systematic review.

Although the health benefits of breastfeeding are acknowledged widely, opinions and recommendations are divided on the optimal duration of exclusive breastfeeding. We systematically reviewed available evidence concerning the effects on child health, growth, and development and on maternal health of exclusive breastfeeding for 6 months vs. exclusive breastfeeding for 3-4 months followed by mixed breastfeeding (introduction of complementary liquid or solid foods with continued breastfeeding) to 6 months. Two independent literature searches were conducted, together comprising the following databases: MEDLINE (as of 1966), Index Medicus (prior to 1966), CINAHL, HealthSTAR, BIOSIS, CAB Abstracts, EMBASE-Medicine, EMBASE-Psychology, Econlit, Index Medicus for the WHO Eastern Mediterranean Region, African Index Medicus, Lilacs (Latin American and Carribean literature), EBM Reviews-Best Evidence, the Cochrane Database of Systematic Reviews, and the Cochrane Controlled Trials Register. No language restrictions were imposed. The two searches yielded a total of 2,668 unique citations. Contacts with experts in the field yielded additional published and unpublished studies. Studies were stratified according to study design (controlled trials vs. observational studies) and provenance (developing vs. developed countries). The main outcome measures were weight and length gain, weight-for-age and length-for-age z-scores, head circumference, iron status, gastrointestinal and respiratory infectious morbidity, atopic eczema, asthma, neuromotor development, duration of lactational amenorrhea, and maternal postpartum weight loss. Twenty independent studies meeting the selection criteria were identified by the literature search: 9 from developing countries (2 of which were controlled trials in Honduras) and 11 from developed countries (all observational studies). Neither the trials nor the observational studies suggest that infants who continue to be exclusively breastfed for 6 months show deficits in weight or length gain, although larger sample sizes would be required to rule out modest increases in the risk of undernutrition. The data are conflicting with respect to iron status but suggest that, at least in developing-country settings, where iron stores of newborn infants may be suboptimal, exclusive breastfeeding without iron supplementation through 6 months of age may compromise hematologic status. Based primarily on an observational analysis of a large randomized trial in Belarus, infants who continue exclusive breastfeeding for 6 months or more appear to have a significantly reduced risk of one or more episodes of gastrointestinal tract infection. No significant reduction in risk of atopic eczema, asthma, or other atopic outcomes has been demonstrated in studies from Finland, Australia, and Belarus. Data from the two Honduran trials suggest that exclusive breastfeeding through 6 months of age is associated with delayed resumption of menses and more rapid postpartum weight loss in the mother. Infants who are breastfed exclusively for 6 months experience less morbidity from gastrointestinal tract infection than infants who were mixed breastfed as of 3 or 4 months of age. No deficits have been demonstrated in growth among infants from either developing or developed countries who are exclusively breastfed for 6 months or longer. Moreover, the mothers of such infants have more prolonged lactational amenorrhea and faster postpartum weight loss. Based on the results of this review, the World Health Assembly adopted a resolution to recommend exclusive breastfeeding for 6 months to its member countries. Large randomized trials are recommended in both developed and developing countries to ensure that exclusive breastfeeding for 6 months does not increase the risk of undernutrition (growth faltering), to confirm the health benefits reported thus far, and to investigate other potential effects on health and development, especially over the long term.

C-peptide levels and the duration of lactational amenorrhea

Changes in insulin sensitivity play an important role in directing metabolic energy toward milk production in lactating mammals. In rats, prolactin causes upregulation of insulin receptors in mammary tissue together with an increase in peripheral insulin resistance, leading to a preferential allocation of energy to support milk production (1, 2). In humans, the shift in energy allocation during lactation away from peripheral tissues and toward milk production is correlated with lower insulin levels (2–4).

Energetics and reproductive effort.

Natural selection favors the optimal allocation of energy and other limiting resources to reproduction. Human reproductive physiology displays characteristic patterns that can be viewed as mechanisms that help optimize reproductive effort in the face of environmental energetic constraints. Female ovarian function is particularly sensitive to energy balance and energy flux, resulting in a synchronization of conception with favorable energetic conditions. Reproductive effort during gestation is highly buffered from environmental energetic constraints, but the duration of gestation and final birthweight are both very sensitive to maternal energy availability. Milk production during lactation is relatively buffered from maternal energetic constraints as well, but the duration of lactational amenorrhea is sensitive to the relative metabolic load of lactation. Male gamete production is very insensitive to energetic constraints, but variation in testosterone production in response to both age and longer-lasting energetic conditions contributes to the modulation of somatic and behavioral aspects of male reproductive effort, aspects that are more energetically costly for a male. There is also new evidence that testosterone may also help to modulate the trade-off between male parenting and mating effort.

Impact of lactational performance on bone mineral density in marginally-nourished Bangladeshi women.

This cross-sectional study, carried out during July 1997-June 1998, evaluated the effects of prolonged breast-feeding and lactational amenorrhoea on bone mineral density (BMD) in 400 marginally-nourished Bangladeshi women aged 20-81 years. A bone densitometer was used for measuring BMD in the distal and ultra-distal end of radius and ulna. The results showed that the women who breastfed for 60 months or less had a higher mean BMD compared to those who breastfed for 61-120 months and for over 120 months. There was a significantly higher BMD in the women who had a shorter duration of lactational amenorrhoea compared to those having a longer duration of lactational amenorrhoea. BMD was significantly and negatively correlated with total duration of lactational amenorrhoea (slope -0.024, p<0.05) after controlling for parity, physical workload, and total duration of breast-feeding. The study concluded that there was a negative correlation between longer duration of breast-feeding and BMD, but it was not found when other factors were controlled in multivariate analysis. The duration of lactational amenorrhoea, which is a proxy indicator of breast-feeding, showed a negative correlation with BMD. It is recommended that all lactating women be given diet with adequate calcium to support breast-feeding for maintaining good nutrition of their bones.

THE DURATION OF LACTATIONAL AMENORRHOEA IN URBAN BANGLADESHI WOMEN

The duration of lactational amenorrhoea, and infant feeding patterns and behaviour, were investigated in a sample of 97 mother-infant pairs living in a poor urban area of Dhaka, Bangladesh. A seven-hour time allocation method was used to determine the number of breast-feeding bouts and their duration. The seven-hour observation period was conducted on five occasions: at birth, 1 month, 4 months, 8 months and either 10 or 11 months. The median duration of lactational amenorrhoea was determined to be 24.07 weeks using survival analysis. Mothers who breast-fed their babies for longer and more frequently had, on average, a longer period of lactational amenorrhoea. There was no relationship between sociodemographic characteristics of the mother and duration of lactational amenorrhoea, nor was there any significant relationship between maternal anthropometry and birth weight of the baby and duration of lactational amenorrhoea, but there was a tendency for women with lower body mass index to have longer durations. Using the Cox proportional hazards model, the best predictor of duration of lactational amenorrhoea was the mean of months 0 and 1 durations of breast-feeding, adjusted for the mean frequencies for those months. The introduction of weaning food was also an important predictor.

Effects of Nutritional Status and Supplementation on Resumption of Menstruation Amongst Parturient Nigerian Women

Context: Breastfeeding patterns, ethnic variation and nutrition have been shown to influence the return of menstruation after childbirth, but the role played by nutritional status requires further elucidation, particularly in a place like Nigeria where undernutrition is common. Objectives: To determine the effects of nutrition and breastfeeding pattern on the duration of lactational amenorrhoea in Nigerian women. Subjects and Methods: Marginally malnourished mothers (162) were randomised into two groups [A & B] for comparison with a third group [C] of well-nourished mothers. Mothers in Group A (83 subjects) received supplements in the form of specially formulated biscuits while those in Group B (79 women) & Group C (85 women) received none. The subjects were visited 3 times a week to ensure compliance with the supplements and to collect information on breastfeeding pattern and duration of lactational amenorrhoea. Results: There were no significant differences in the duration of postpartum amenorrhoea in the three groups of mothers, being 270, 220 and 234 days for Groups A, B and C respectively. Wide individual variations were observed in the duration of amenorrhoea in each group of mothers despite the fact that they generally had similar patterns of breastfeeding. The energy expenditure patterns in the supplemented and unsupplemented mothers were similar. Conclusion: Nutritional status and supplementation do not seem to influence the duration of lactational amenorrhoea in this group of Nigerian women. Subtle physiological differences between individual women may account for the wide individual variations observed in the time of resumption of menstruation after childbirth in the subjects. Key Words: Breastfeeding, Lactational Amenorrhoea, Nutritional Status, Menstruation. [Trop J Obstet Gynaecol, 2002, 19: 39-43].

Plasma prolactin/oestradiol ratio at 38 weeks gestation predicts the duration of lactational amenorrhoea.

Fully breastfeeding women experience an amenorrhoea of variable duration. Our aim was to identify in pregnancy, endocrine markers that could predict the duration of subsequent lactational amenorrhoea. We studied 17 healthy women at 34 and 38 weeks gestation, and 1 and 3 months post-partum. The women fully breastfed until 6 months post-partum. During pregnancy, prolactin (PRL), oestrogens (total oestradiol, unconjugated oestrone, unconjugated oestriol), sex hormone binding globulin (SHBG), dehydroepiandrosterone sulphate (DHEA-S), progesterone and placental lactogen, and during post-partum PRL, oestrogens and SHBG, were measured. Free oestradiol in pregnancy and post-partum was calculated. Ten women experienced long (>6 months) and seven experienced short (<6 months) lactational amenorrhoea. At 38 weeks gestation, the women who experienced a long lactational amenorrhoea had twice as much PRL, about half the total oestradiol, lower SHBG concentration (P < 0.05, Student's t-test, Bonferroni modification) and similar free oestradiol concentration, compared with those who experienced short lactational amenorrhoea. The difference in PRL concentration persisted in post-partum postsuckling samples. At 38 weeks gestation, the ratio PRL/oestradiol identified all individual women according to the subsequent duration of their lactational amenorrhoea, suggesting that duration of lactational amenorrhoea is conditioned during pregnancy.

An analysis of breastfeeding patterns and menses returning in Chengdu, China.

To study the relationship between infant feeding practices and the duration of lactational amenorrhea, WHO conducted a multi-centered prospective study in 7 countries from 1989. This paper reports the preliminary results based on the data collected in Chengdu center in China. A detailed follow-up survey was conducted among 541 pairs of mothers and infants from delivery to the returning of menses of mothers at the interval of every 2 weeks. The results showed that the mean number of breastfeeding episodes and mean duration of breastfeeds had little correlation with the time since delivery. Within 6 months since delivery, the percentage of infants' feeds consisting of breastmilk was over 90%, and this percentage dropped to 70% at 1 year's age of infants. The time to the start of regular supplementation was 153 days postpartum. The proportion of women in exclusive breastfeeding at 2 weeks postpartum was 73.4%, and these figures at 3 and 6 months postpartum were about 60% and 40%, respectively. Until 18 months postpartum, nearly 80% mothers were partial breastfeeding their infants. The cumulative probabilities of menses returning were 0.0150, 0.0395, 0.2345 and 0.6820 at 61, 89, 187 and 369 days postpartum respectively. The median duration of lactational amenorrhea was 282 days. These results indicated that the duration of lactational amenorrhea would be prolonged if the time of exclusive/predominant breastfeed was extended and the supplementary food was introduced later. The paper concluded that the first menses returning was the signal for initiating contraceptive methods for women.

Post-suckling prolactin:oestradiol ratio--a potential index to predict the duration of lactational amenorrhoea in women.

To assess whether the duration of lactational amenorrhoea can be predicted in individual women, we studied the pre- and post-suckling concentrations of immune prolactin (IR-PRL) and of bioactive prolactin (BIO-PRL) and basal concentrations of oestradiol in ten amenorrhoeic fully nursing women at 3 months post-partum. The women were of similar age, weight and had infants of similar growth rate. Five of these women were to experience long amenorrhoea (>180 days) and the others short amenorrhoea (<180 days). Blood samples were drawn 30 min after a suckling episode initiated at 0800 h, 1600 h and 2400 h. BIO-PRL distinguished between groups of women at 0030 h but not at other times, while there was considerable overlap between values for IR-PRL and oestradiol at all times studied. At 1630 h, the ratios post-suckling BIO-PRL: oestradiol and post-suckling IR-PRL:oestradiol were above 2000 in the women that were to experience long amenorrhoea and below this threshold in the other women. The ratio post-suckling BIO-PRL:oestradiol provided more information since the difference between the lowest ratio in the long amenorrhoea and the highest ratio in the short was 699, while it was 520 for the IR-PRL:oestradiol ratio. The determination of these ratios may help to predict the duration of lactational amenorrhoea in individual fully nursing women.

Effects of age at introduction of complementary foods to breast-fed infants on duration of lactational amenorrhea in Honduran women

Lactational amenorrhea (LA) is associated with postpartum infertility and is known to be related to breast-feeding frequency and duration, but the exact role of complementary feeding of the infant has not been clearly defined. Data on LA were collected during and after a 2-mo intervention trial in which low-income Honduran women who had breast-fed fully for 4 mo were randomly assigned to one of three groups: continued full breast-feeding until 6 mo (FBF, n = 50), introduction of complementary foods at 4 mo with ad libitum breast-feeding from 4 to 6 mo (SF, n = 47), or introduction of complementary foods at 4 mo with maintenance of baseline breast-feeding frequency from 4 to 6 mo (SF-M, n = 44). Women were followed up until the infant was 12 mo of age, or later if menses had not occurred by then. All but six of the women continued to breast-feed for > or = 12 mo. With the exclusion of those whose menses returned before 18 wk postpartum (which could not have been due to the intervention), the proportion of women who were amenorrheic at 6 mo was 64.5% in the SF group, 80.0% in the FBF group, and 85.7% in the SF-M group (chi-square test = 4.13, P = 0.02; one-tailed test with the latter two groups combined). The total duration of LA did not differ significantly among groups. The most significant determinant of LA was time spent breast-feeding (min/d), which was in turn negatively associated (P = 0.06) with the infant's energy intake from complementary foods in regression analyses. These results indicate that there is a significant effect of introducing foods at 4 mo on the likelihood of amenorrhea at 6 mo postpartum, but not thereafter, and that this effect is not seen in mothers who maintain breast-feeding frequency.

Sucking pressure and its relationship to milk transfer during breastfeeding in humans.

Breast sucking pressure has been only partially characterized in humans and its quantitative relationships with milk transfer and endocrine maternal responses are unknown. A method to record sucking pressure and milk transfer during complete sucking episodes is described. A tubing connected at one end to a pressure transducer was attached to the nipple so that the baby sucked both the nipple and the catheter during breastfeeding. The transducer's signals were fed into a commercial computer system designed to digitize and analyse physiological signals. A total of 27 recordings, 13 of which were from a single breast and 14 from both breasts were evaluated. Average values for the mean and maximum sucking pressures were -50 and -197 mmHg, respectively; the median intersuck interval was 0.7 s; and duration of the sucking episode was 7 min. Diverse sucking pressure patterns were observed due to different mixes of sucking bursts with steady sucking and stable versus decreasing pressure and frequency throughout each sucking episode. The amount of milk transferred to the baby was estimated from the difference in body weight immediately before and after each episode. Milk transfer from the second breast was 58% lower than from the first; this was associated with a significant decrease in grams of milk transferred per suck or per minute without significant changes in sucking pressure. The data suggest that there is a change in the maternal physiological response to sucking between the first and second breast. This report shows the feasibility of measuring the sucking pressure developed by human babies during complete nursing episodes, and offers great potential to explore the relationships between the physical parameters of sucking and maternal physiological responses, such as hormonal changes, milk yield and duration of lactational amenorrhoea.

Diminished luteinizing hormone biopotency in breastfeeding women.

The effect of nursing on plasma luteinizing hormone bioactivity (B-LH) and immunoactivity (I-LH) was assessed at 4 and 6 months post partum in fully nursing women who experienced their first bleeding between months 5 and 6 post partum (n = 6, short amenorrhoea) or after the month 6 (n = 10, long amenorrhoea). Controls were 10 non-nursing fertile women. Blood samples were drawn twice weekly at month 4 post partum and at month 6 post partum. In the nursing women who were cycling at month 6 and in non-nursing women samples were drawn during the follicular phase. I-LH was measured by a time resolved immunofluorometric assay (DELFIA) and B-LH by the mouse Leydig cell assay. Nursing decreased B-LH more than I-LH resulting in a relationship between B-LH and I-LH different to that of non-nursing women (B-LH = 2.84 x I-LH-0.16 and B-LH = 4.27 x I-LH + 3.11 respectively, P < 0.05, by likelihood test). Plasma B-LH or I-LH were similar in nursing women with short or long amenorrhoea. In conclusion, nursing alters the quality of circulating LH, however, the decreased LH steroidogenic potency does not play a role in determining the duration of lactational amenorrhoea.