Prenatal Weeks Research Articles

Association between prenatal air pollutant exposure and autism spectrum disorders in young children: A matched case-control study in Canada

The direction and magnitude of association between maternal exposure to ambient air pollutants across gestational windows and offspring risk of autism spectrum disorders (ASD) remains unclear. We sought to evaluate the time-varying effects of prenatal air pollutant exposure on ASD. We conducted a matched case-control study of singleton term children born in Ontario, Canada from 1-Apr-2012 to 31-Dec-2016. Provincial birth registry data were linked with applied behavioural analysis services and ambient air pollutant datasets to ascertain prenatal exposure to nitrogen dioxide (NO2), ground-level ozone (O3), fine particulate matter (PM2.5), and ASD diagnoses. Covariate balance between cases and controls was established using coarsened exact matching. Conditional logistic regression was used to assess the association between prenatal air pollutant exposure and ASD. Distributed lag non-linear models (DLNM) were used to examine the effects of single-pollutant exposure by prenatal week. Sensitivity analyses were conducted to assess the impact of exposure period on the observed findings. The final sample included 1589 ASD cases and 7563 controls. Compared to controls, cases were more likely to be born to mothers living in urban areas, delivered by Caesarean section, and assigned male sex at birth. NO2 was a consistent and significant contributor to ASD risk after accounting for co-exposure to O3, PM2.5 and covariates. The odds ratio per interquartile range increase was 2.1 (95%CI 1.8–2.3) pre-conception, 2.2 (2.0–2.5) for the 1st trimester, 2.2 (1.9–2.5) for the 2nd trimester, and 2.1 (1.9–2.4) for the 3rd trimester. In contrast, findings for O3 and PM2.5 with ASD were inconsistent. Findings from DLNM and sensitivity analyses were similar. Exposure to NO2 before and during pregnancy was significantly associated with ASD in offspring. The relationship between prenatal O3 and PM2.5 exposure and ASD remains unclear. Further investigation into the combined effects of multi-pollutant exposure on child neurodevelopment is warranted.

Morphologies in-between: The impact of the first steps on the human talus.

The development of bipedalism is a very complex activity that contributes to shaping the anatomy of the foot. The talus, which starts ossifying in utero, may account for the developing stages from the late gestational phase onwards. Here, we explore the early development of the talus in both its internal and external morphology to broaden the knowledge of the anatomical changes that occur during early development. The sample consists of high-resolution microCT scans of 28 modern juvenile tali (from 36 prenatal weeks to 2 years), from a broad chronological range from the Late Roman period to the 20th century. We applied geometric morphometric and whole-bone trabecular analysis to investigate the early talar morphological changes. In the youngest group (<6 postnatal months), the immature external shell is accompanied by an isotropic internal structure, with thin and densely packed trabeculae. After the initial attempts of locomotion, bone volume fraction decreases, while anisotropy and trabecular thickness increase. These internal changes correspond to the maturation of the external shell, which is now more defined and shows the development of the articular surfaces. The internal and external morphology of the human talus reflects the diverse load on the foot during the initial phases of the bipedal locomotion, with the youngest group potentially reflecting the lack of readiness of the human talus to bear forces and perform bipedal walking. These results highlight the link between mechanical loading and bone development in the human talus during the acquisition of bipedalism, providing new insight into the early phases of talar development.

Quantitative anatomy of primary ossification centres of the lateral and basilar parts of the occipital bone in the human foetus.

Computed tomography (CT)-based quantitative analysis of primary ossification centres in the cranium has not been carried out to date due to the limited availability of the foetal human material. Detailed morphometric data about the development of primary ossification centres in human foetuses may be useful in the early detection of developmental defects. Understanding the growth and development of the occipital bone is crucial in assessing the normal and pathological development of the cranial base, and the cranium as a whole. The study material comprised 37 human foetuses (16 males and 21 females) aged 18-30 weeks of gestation. Using CT, digital image analysis software, three-dimensional reconstruction and statistical methods, the size of the primary ossification centres of the lateral and basilar parts of the occipital bone was evaluated. The morphometric characteristics of primary ossification centres of the lateral and basilar parts of the occipital bone display neither sex nor laterality differences. These ossification centres grow linearly with respect to their sagittal and transverse diameters, projection surface area and volume. The obtained morphometric data of primary ossification centres in the lateral and basilar parts of the occipital bone may be considered as normative for their respective prenatal weeks and may contribute to the estimation of gestational ages and the diagnostics of congenital defects.

Qualitative and quantitative dermatoglyphics of chronic kidney disease of unknown origin (CKDu) in Sri Lanka

BackgroundDermatoglyphics has been used widely in fields of medicine as a non-invasive diagnostic tool and an early assessment of risk for certain medical conditions. It reflects disturbances in fetal development during early prenatal weeks 14–22 when fingerprints develop. Dermatoglyphic asymmetry has been used to measure developmental instability during a specific period of human fetal development. Thus, the present study was planned to investigate whether digital and palmar dermatoglyphics of chronic kidney disease of unknown origin (CKDu) patients in Sri Lanka are different from healthy people.MethodsA case control study was carried out among CKDu patients (90 males, 90 females) from a CKDu endemic area and gender-matched two control groups; one group from a CKDu endemic region (90 males, 90 females) and another group from a CKDu non-endemic region (90 males, 90 females). Dermatoglyphics were obtained using photographic methods. Both qualitative and quantitative dermatoglyphic variables were defined and analyzed according to standard criteria. Both directional (DA) and fluctuating asymmetry (FA) were assessed.ResultsSeveral qualitative dermatoglyphic variables had significant association with CKDu. The triradii a1 variable was less evident in palms of CKDu cases in both genders when compared to both control groups. The FA of pattern discordance (right vs left hands) between CKDu cases and control group were significant in several digits. The FA of the ridge count was found significant in several digits, and also significant for A-B ridge count and total ridge count.ConclusionBased on these results, it is proposed that the mechanisms responsible for the development of CKDu might be associated with those responsible for FA observed in CKDu patients. Accordingly, a diagnostic tool based on FA could be developed for predicting risk prior to the development of CKDu.

Morphometric study of the primary ossification center of the fibular shaft in the human fetus

PurposesPrecise morphometric data on the development of ossification centers in human fetuses may be useful in the early detection of skeletal dysplasias associated with delayed ossification center development and mineralization. The present study was performed to quantitatively examine the primary ossification center of the fibular shaft with respect to its linear, planar and volumetric parameters.Materials and methodsUsing methods of CT, digital-image analysis (Osirix 3.9 MD) and statistics (Student’s t-test, Shapiro–Wilk, Fisher’s test, Tukey’s test, Kruskal–Wallis test, regression analysis), the size of the primary ossification center of the fibular shaft in 47 spontaneously aborted human fetuses (25 ♂ and 22 ♀) aged 17–30 weeks was studied. In each fetus, the assessment of linear dimensions (length, transverse diameters for: proximal end, middle part and distal end), projection surface area and volume of the fibular shaft ossification center was carried out.ResultsWith no sex and laterality differences, the best fit growth dynamics for the primary ossification center of the fibular shaft was modelled by the following functions: y = − 13.241 + 1.567 × age ± 1.556 (R2 = 0.94) for its length, y = − 0.091 + 0.063 × age ± 0.073 (R2 = 0.92) for its proximal transverse diameter, y = − 1.201 + 0.717 × ln(age) ± 0.054 (R2 = 0.83) for its middle transverse diameter, y = − 2.956 + 1.532 × ln(age) ± 0.090 (R2 = 0.89) for its distal transverse diameter, y = − 69.038 + 4.699 × age ± 4.055 (R2 = 0.95) for its projection surface area, and y = − 126.374 + 9.462 × age ± 8.845 (R2 = 0.94) for its volume.ConclusionsThe ossification center in the fibular shaft follows linear functions with respect to its length, proximal transverse diameter, projection surface area and volume, and natural logarithmic functions with respect to its middle and distal transverse diameters. The obtained morphometric data of the fibular shaft ossification center is considered normative for their respective prenatal weeks and may be of relevance in both the estimation of fetal age and the ultrasound diagnostics of congenital defects.

Quantitative anatomy of the ulna\u2019s shaft primary ossification center in the human fetus

PurposeThere has been little information in the medical literature regarding the growing ulna in the human fetus, though such knowledge appears to be potentially useful in diagnosing skeletal dysplasias, characterized by a disrupted or completely halted growth of the fetus. Therefore, longitudinal measurements of long bones are extremely conducive in assessing both pregnancy and fetal anatomy.Materials and methodsUsing methods of CT, digital-image analysis and statistics, the size of the ulna’s shaft primary ossification center in 48 (26 males and 22 females) spontaneously aborted human fetuses aged 17–30 weeks was studied.ResultsWith no sex differences, the best fit growth dynamics for the ulna’s shaft primary ossification center was modeled by the following functions: y = − 8.476 + 1.561 × age ± 0.019 for its length, y = − 2.961 + 0.278 × age ± 0.016 for its proximal transverse diameter, y = – 0.587 + 0.107 × age ± 0.027 for its middle transverse diameter, y = − 2.865 + 0.226 × age ± 0.295 for its distal transverse diameter, y = − 50.758 + 0.251 × (age)2 ± 0.016 for its projection surface area, and y = − 821.707 + 52.578 × age ± 0.018 ± 102.944 for its volume.ConclusionsThe morphometric characteristics of the ulna’s shaft primary ossification center show neither sex nor bilateral differences. The ulna’s shaft primary ossification center grows linearly with respect to its length, transverse dimensions and volume, and follows a quadratic function with respect to its projection surface area. The obtained morphometric data of the ulna’s shaft primary ossification center is considered normative for respective prenatal weeks and may be of relevance in both the estimation of fetal ages and the diagnostic process of congenital defects.

Quantitative anatomy of the ilium\u2019s primary ossification center in the human fetus

PurposeAn understanding of the development of the ilium’s primary ossification center may be useful in both determining the fetal stage and maturity, and for detecting congenital disorders. This study was performed to quantitatively examine the ilium’s primary ossification center with respect to its linear, planar and volumetric parameters.Materials and methodsUsing methods of CT, digital-image analysis and statistics, the size of the ilium’s primary ossification center in 42 spontaneously aborted human fetuses of crown–rump length (CRL) ranged from 130 to 265 mm (aged 18–30 weeks) was studied.ResultsWith no sex and laterality differences, the best fit growth dynamics for the ilium’s primary ossification center was modelled by the following functions: y = − 63.138 + 33.413 × ln(CRL) ± 1.609 for its vertical diameter, y = − 59.220 + 31.353 × ln(CRL) ± 1.736 for its transverse diameter, y = − 105.681 + 1.137 × CRL ± 16.035 for its projection surface area, and y = 478.588 + 4.035 × CRL ± 14.332 for its volume. The shape of the ilium’s primary ossification center did not change over the study period, because its transverse -to- vertical diameter ratio was stable at the level of 0.94 ± 0.07.ConclusionsThe size of the ilium’s primary ossification center displays neither sex nor laterality differences. The ilium’s primary ossification center grows logarithmically with respect to its vertical and transverse diameters, and linearly with respect to its projection surface area and volume. The shape of the ilium’s primary ossification center does not change throughout the examined period. The obtained quantitative data of the ilium’s primary ossification center is considered normative for respective prenatal weeks and may contribute to the prenatal ultrasound diagnostics of congenital defects.

Quantitative anatomy of the primary ossification center of the femoral shaft in human fetuses

PurposeEarly clinical distinction of congenital defects in the femur is extremely important, as it determines the prognosis of the development of the lower limb. This study was performed to quantitatively examine the primary center of ossification in the femoral shaft with respect to its linear, planar, and volumetric parameters.Materials and methodsUsing methods of CT, digital-image analysis, and statistics, the size of the primary ossification center of the femoral shaft in 47 spontaneously aborted human fetuses aged 17–30 weeks was studied.ResultsWith no sex and laterality differences, the best fit growth dynamics for femoral shaft ossification center was modelled by the following functions: y = 5.717 + 0.040 × (age)2 ± 2.905 (R2 = 0.86) for its length, y = −3.579 + 0.368 × age ± 0.529 (R2 = 0.88) for its proximal transverse diameter, y = −1.105 + 0.187 × age ± 0.309 (R2 = 0.84) for its middle transverse diameter, y = −2.321 + 0.323 × age ± 0.558 (R2 = 0.83) for its distal transverse diameter, y = −50.306 + 0.308 × (age)2 ± 18.289 (R2 = 0.90) for its projection surface area, and y = −91.458 + 0.390 × (age)3 ± 92.146 (R2 = 0.88) for its volume.ConclusionsThe size of the femoral shaft ossification center displays neither sex nor laterality differences. The ossification center in the femoral shaft follows quadratic functions with respect to its length and projection surface area, linear functions with respect to its proximal, middle, and distal transverse diameters, and a cubic function with respect to its volume. The obtained morphometric data of the femoral shaft ossification center are considered normative for respective prenatal weeks and may be of relevance in both the estimation of fetal ages and the ultrasound diagnostics of congenital defects.

Ossification center of the humeral shaft in the human fetus: a CT, digital, and statistical study

PurposeThe knowledge of the development of the humeral shaft ossification center may be useful both in determining the fetal stage and maturity and for detecting congenital disorders, as well. This study was performed to quantitatively examine the humeral shaft ossification center with respect to its linear, planar, and volumetric parameters.Materials and methodUsing methods of CT, digital image analysis, and statistics, the size of the humeral shaft ossification center in 48 spontaneously aborted human fetuses aged 17–30 weeks was studied.ResultsWith no sex differences, the best-fit growth dynamics for the humeral shaft ossification center was modeled by the following functions: y = −78.568 + 34.114 × ln (age) ± 2.160 for its length, y = −12.733 + 5.654 × ln(age) ± 0.515 for its proximal transverse diameter, y = −4.750 + 2.609 × ln (age) ± 0.294 for its middle transverse diameter, y = −10.037 + 4.648 × ln (age) ± 0.560 for its distal transverse diameter, y = −146.601 + 11.237 × age ± 19.907 for its projection surface area, and y = 121.159 + 0.001 × (age)4 ± 102.944 for its volume.ConclusionsWith no sex differences, the ossification center of the humeral shaft grows logarithmically with respect to its length and transverse diameters, linearly with respect to its projection surface area, and fourth-degree polynomially with respect to its volume. The obtained morphometric data of the humeral shaft ossification center are considered normative for respective prenatal weeks and may be of relevance in both the estimation of fetal ages and the ultrasonic diagnostics of congenital defects.

Mental health trajectories and related factors among perinatal women.

To investigate Taiwanese women's mental health trajectories from the third trimester of pregnancy to four weeks postpartum and the correlations of these trajectories with perceived social support and demographic characteristics. Previous studies have reported differences between prenatal and postpartum mental health status. A repeated design study was conducted in a medical hospital in Southern Taiwan. One-hundred and ninety-four Taiwanese women completed the Chinese Health Questionnaire and Social Support Scale at the 36th prenatal week and first and fourth week postpartum. Three linear mental health trajectories for perinatal women were identified. Consistently poor perinatal mental health was reported by 16·0% of the participants. Less social support was associated with lower prenatal mental health scores. Younger age was a risk factor for consistently poor perinatal health. Vaginal delivery was associated with improved mental health after childbirth. Mental health was worse in the third trimester of pregnancy than postpartum. Less social support was associated with lower prenatal mental health scores, and this association was similarly distributed between women with consistently poor and improved mental health after birth. Health care providers should assess women's mental health status and provide timely interventions during the perinatal period. Social support should be provided for pregnant women, especially younger women or those with lower perceived social support.

Reliable and powerful laboratory markers of cobalamin deficiency in the newborn: plasma and urinary methylmalonic acid

Background: Diagnosing cobalamin deficiency is critical, given the high prevalence of cobalamin deficiency particularly in developing countries. Measuring serum cobalamin levels is of limited diagnostic sensitivity, in other words its specificity and sensitivity are low. The present study investigated the changes in the levels of metabolic markers – plasma homocysteine, plasma methylmalonic acid (MMA) and urinary MMA – of cobalamin metabolism.Methods: Plasma cobalamin and serum folic acid were studied in 206 pregnant women over the last four prenatal weeks. Plasma cobalamin, folic acid, homocysteine, MMA from umbilical cord blood and urinary MMA in newborns were studied.Results: Plasma cobalamin values were low in 66% of the mothers. There was a positive correlation between maternal and neonatal plasma cobalamin values (r = 0.72, p < 0.001). B12 was strongly inversely associated with plasma MMA, urine MMA and plasma homocysteine. To predict cobalamin deficiency, sensitivities of plasma MMA, urinary MMA and homocysteine were 96.4%, 95.6% and 88.2%, respectively. And positive predictive values (PPV) were 96.2%, 96.9% and 86% for plasma MMA, urinary MMA and plasma homocysteine levels, respectively.Conclusion: Plasma MMA and urinary MMA B12 are the most robust markers of cobalamin deficiency. As a non-invasive method, urinary MMA is a sensitive method in demonstrating cobalamin deficiency in the newborn.

A case of prenatally detected hepatic cyst communicating with the hepatic duct

Here, we describe the case of a 9-year-old girl. During the patient's prenatal period, her mother had suffered domestic violence perpetrated by the patient's father. On maternal ultrasonography and magnetic resonance imaging, an intraabdominal cystic lesion was detected in the fetus at around the 30th prenatal week. The patient was delivered normally, and there were no evident anomalies on her body. Computed tomography with drip infusion cholangiography and percutaneous retrograde transhepatic cholangiography demonstrated an intrahepatic cyst of approximately 3 cm in diameter, which was located at S 5 –S 8 and communicated with the confluence of the bilateral hepatic ducts. The cyst is clinically conjectured to be a solitary intrahepatic biliary cyst. However, it remains possible that the cyst is a ciliated hepatic foregut cyst or indicates hepatic injury that may have occurred as a result of domestic violence to the mother. Careful, long-term observation of the patient will be continued to ensure that any malignant transformation is not missed. • This is an extremely rare case of prenatally detected intrahepatic cyst. • The cyst had a communication with the bile duct. • MRI and DIC-CT indicated the presence of the communication. • Percutaneous transhepatic cholangiography proved the communication. • Solitary intrahepatic biliary cyst is currently suspected.

Expression of GABA transporter (GAT-1) and GLIAL FIDRILLAR ACIDIC PROTEIN (GFAP) in maturated human neocortex

GABA transporter (GAT-1) distribution in the human neocortex sulcuses (fetus from 14 weeks prenatal till four years old human) was researched by immunohistochemistry method. Intensive GAT-1 positive staining in the fissure lip from fetus neocortex was detected. GAT-1 positive staining decreased with different intensivity in the sulcuses and in the straight surfaces of neocortex, depended of fetus age. After birth the lips and the straight surfaces of neocortex was stained uniform, but was kept the decay of labeling in the fissures. From 26 till 33 prenatal weeks GAT-1 positive terminals innervated subventricular/ventricular zone, where they blocked cell progenitor proliferation, whereby triggered the astrocytic differentiation.

A Rare Case of Congenital Choroid Plexus Carcinoma

We report a 1-year-old child with the prenatal (week 29 + 5) diagnosis of a brain tumor. The parents were informed about all aspects of prognosis and options concerning termination of pregnancy. The parents opted for an aggressive therapeutic approach after extensive and informative case conferences and counseling. The histopathological diagnosis after partial tumor resection was choroid plexus carcinoma, two weeks thereafter tumor size was progressive. The parents opted for palliative treatment at this stage. The patient died at the age of one year. Ethical aspects have to be actively considered and addressed when caring for children with choroid plexus carcinoma.

A case of conjoined twin's cephalothoracopagus janiceps disymmetros

Conjoined twins are rare variants of monozygotic twins, which result from an incomplete late division of the embryonic disk. Here we report the rarest case of conjoined twins – the male cephalothoracopagus janiceps disymmetros – born in prenatal week 30, from the archive of the Department of Teratology of the Institute of Experimental Medicine AS CR in Prague. The crown-rump length of each twin, 21 cm, corresponded to prenatal week 22 in a normal gravidity. The head, chest and upper portion of the abdomen of the twins were fused. The anatomical features of these extremely rare conjoined twins and the observed external anomalies as a narrow nose with a single nostril, male hypoplastic genitalia, partially duplicated sella turcica, spina bifida and further abnormalities are described and documented.

Early development of the lower deciduous dentition and oral vestibule in human embryos

The aim of this work was to investigate the early development of the deciduous dentition and oral vestibule in the human embryonic lower jaw. Histological sections and three-dimensional reconstructions from prenatal weeks 6-9 were used. A continuous anlage for the oral vestibule did not exist in the mandible. In contrast to the upper jaw, where we previously observed that the dental and vestibular epithelia developed separately, two dento-vestibular bulges differentiated in the incisor region of the mandible. The lingual parts of each bulge were found to give rise to the respective central and lateral incisors, whereas the labial parts differentiated into the vestibular epithelium. In the canine and molar areas, the dental and vestibular epithelia originated separately. Later, the segments of the vestibular epithelium fused into the labial vestibular ridge, giving rise to the lower oral vestibule in the lip region. In the cheek region, the oral vestibule was found to originate in the mucosal inflection between the developing jaw and the cheek. A similar heterogeneous developmental base for the oral vestibule was also observed in the upper jaw. There is thus no general scheme for the early development of the dental and vestibular epithelia that applies to both the upper and lower jaws, and to both their anterior and posterior regions.

First localization and biochemical identification of chromogranin B- and secretoneurin-like immunoreactivity in the fetal human vagal/nucleus solitary complex

The human vagal/nucleus solitary complex is a primary visceral relay station and an integrative brain stem area which displays a high density of chromogranin B- and secretoneurin-like immunoreactivity. In this study, we localized and biochemically identified these proteins during prenatal development. At prenatal week 11, 15, 20 and 37, we performed a chromatographic analysis to identify the molecular forms of PE-11, a peptide within the chromogranin B sequence, and secretoneurin, a peptide within secretogranin II. Their localization was studied with immunocytochemistry, and was compared to that of substance P which is well established as a functional neuropeptide in the vagal/nucleus solitary complex. At prenatal week 11, chromogranin B-, secretoneurin- and substance P-like immunoreactivities were detected consisting of varicosities, varicose fibers and single cells. At the same time, PE-11 and secretoneurin appeared as a single peak in chromatographic analysis. Prohormone convertases PC1- and PC2-like immunoreactivities were also present at week 11. In general, the density for each peptide increased during later fetal stages with the highest density at week 37. These results demonstrate that each chromogranin peptide is expressed during human fetal life in neurons of the vagal/nucleus solitary complex indicating that these peptides could be important during prenatal development.

Origin of the Deciduous Upper Lateral Incisor and its Clinical Aspects

The upper lateral incisor in humans is often affected by dental anomalies that might be explained developmentally. To address this question, we investigated the origin of the deciduous upper lateral incisor (i2) in normal human embryos at prenatal weeks 6-8. We used serial frontal histological sections and computer-aided 3D reconstructions. At embryonic days 40-42, two thickenings of the dental epithelia in an "end-to-end" orientation were separated by a groove at the former fusion site of the medial nasal and maxillary processes. Later, these dental epithelia fused, forming a continuous dental lamina. At the fusion site, i2 started to develop. The fusion line was detectable on the i2 germ until the 8th prenatal week. The composite origin of the i2 may be associated with its developmental vulnerability. From a clinical aspect, a supernumerary i2 might be a form of cleft caused by a non-fusion of the dental epithelia.

The Impact of Fatigue on the Development of Postpartum Depression

Previous research suggests early postpartum fatigue (PPF) plays a significant role in the development of postpartum depression (PPD). Predicting risk for PPD via early identification of PPF may provide opportunity for intervention. To replicate and extend previous studies concerning the impact of PPF on symptoms of PPD and to describe the relationships among PPF, PPD, and other variables using the theory of unpleasant symptoms. Correlational, longitudinal study. Participants' homes. Convenience sample of 42 community-dwelling women recruited before 36 weeks of pregnancy. PPF, depressive symptoms, and stress measured during prenatal weeks 36 to 38, and on Days 7, 14, and 28 after childbirth. Salivary cortisol was measured as a physiological marker of stress. Significant correlations were obtained between PPF and symptoms of PPD on Days 7, 14, and 28, with Day 14 PPF levels predicting future development of PPD symptoms in 10 of 11 women. Perceived stress, but not cortisol, was also correlated with symptoms of PPD on Days 7, 14, and 28. Women with a history of depression had elevated depression scores compared to women without, but no variable was as effective at predicting PPD as PPF. Fatigue by Day 14 postpartum was the most predictive variable for symptoms of PPD on Day 28 in this population.

Developmental Acquisition of Voltage-Dependent Conductances and Sensory Signaling in Hair Cells of the Embryonic Mouse Inner Ear

How and when sensory hair cells acquire the remarkable ability to detect and transmit mechanical information carried by sound and head movements has not been illuminated. Previously, we defined the onset of mechanotransduction in embryonic hair cells of mouse vestibular organs to be at approximately embryonic day 16 (E16). Here we examine the functional maturation of hair cells in intact sensory epithelia excised from the inner ears of embryonic mice. Hair cells were studied at stages between E14 and postnatal day 2 using the whole-cell, tight-seal recording technique. We tracked the developmental acquisition of four voltage-dependent conductances. We found a delayed rectifier potassium conductance that appeared as early as E14 and grew in amplitude over the subsequent prenatal week. Interestingly, we also found a low-voltage-activated potassium conductance present at E18, approximately 1 week earlier than reported previously. An inward rectifier conductance appeared at approximately E15 and doubled in size over the next few days. We also noted transient expression of a voltage-gated sodium conductance that peaked between E16 and E18 and then declined to near zero at birth. We propose that hair cells undergo a stereotyped developmental pattern of ion channel acquisition and that the precise pattern may underlie other developmental processes such as synaptogenesis and functional differentiation into type I and type II hair cells. In addition, we find that the developmental acquisition of basolateral conductances shapes the hair cell receptor potential and therefore comprises an important step in the signal cascade from mechanotransduction to neurotransmission.