Abstract
To evaluate whether women with anaemia or high haemoglobin (Hb) in early pregnancy would be at higher risk of miscarriage, this population-based cohort study involved 9453 women whose pregnancies were monitored at primary care centres between 2007 and 2012. The computerised clinical histories were used to collect: Hb measurements (up to 14 weeks of gestation), miscarriage before or by 24 weeks of gestation, and other maternal characteristics. The relation between anaemia (Hb < 110 g/L), normal Hb (110–140 g/L, reference), and high Hb concentrations (≥140 g/L) with miscarriage were expressed as adjusted OR with 95%CI. Restricted cubic spline models were applied to evaluate the dose-response relationships. A total of 520 (5.5%) women were recorded as having a miscarriage. The rate of miscarriage in anaemia, normal Hb, and high Hb concentrations was 8.4%, 5.1%, and 10.2%, respectively. Compared with women with normal Hb at the first trimester, the multivariable-adjusted OR for miscarriage was 2.11 (95%CI, 1.38–3.21) for women with anaemia and 1.83 (95%CI, 1.29–2.58) for women with high Hb. Hb concentrations showed a U-shaped association with miscarriage, with the lowest incidence among women with Hb of 120–130 g/L. These data highlight the importance of considering anaemia and high Hb levels in early pregnancy as harmful indicators for miscarriage.
Highlights
Miscarriage, 85% of which may happen during the first trimester, is one of the most common adverse pregnancy outcomes [1,2]
Motivated by the possibility that the associations observed were due to confounding factors, we investigated whether the effect of Hb on miscarriage differed by factors strongly related to pregnancy loss, such as pregnancy BMI (
Compared to women with normal Hb concentrations, women with anaemia smoked less and were more likely to have a higher number of previous births, pregnancies, and abortions; women with high Hb concentrations were older, had higher body weight and BMI, were less likely to be a smoker, and had fewer deliveries
Summary
Miscarriage, 85% of which may happen during the first trimester, is one of the most common adverse pregnancy outcomes [1,2]. The cause of most miscarriages remains unknown, they presumably result from a complex interplay of non-modifiable and modifiable risk factors [3,4]. It has been suggested that 50% of miscarriages, especially those of the first trimester, are attributed to chromosomal abnormalities [5,6]; other maternal factors may play a role. It is essential, in order to guide future public health policies, to identify risk factors prior to and during pregnancy. Well-known risk factors include advanced age, pre-existing comorbidities (obesity, diabetes, or hypertension), previous miscarriages, smoking, or inappropriate nutritional status [3,9,11]
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