Preconception Hb concentration and risk of preterm birth in over 2·7 million Chinese women aged 20–49 years: a population-based cohort study

Abstract

Evidence on the association between maternal Hb concentration and preterm birth (PTB) risk is inconclusive. This paper aimed to explore whether women with anaemia or high Hb level before pregnancy would be at higher risk of PTB. We conducted a population-based cohort study with 2 722 274 women aged 20-49 years, who participated in National Free Pre-Pregnancy Checkups Project between 2013 and 2015 and delivered a singleton before 2016 in rural China. Logistic models were used to estimate OR and 95 % CI after adjusting for confounding variables. Restricted cubic spline models were applied to evaluate the dose-response relationships. A total of 192 819 (7·08 %) women had preterm deliveries. Compared with women with Hb of 110-149 g/l, the multivariable-adjusted OR for PTB was 1·19 (95 % CI 0·98, 1·44) for women with Hb<70 g/l, 1·01 (95 % CI 0·97, 1·03) for 70-99 g/l, 0·96 (95 % CI 0·95, 0·98) for 100-109 g/l, 1·04 (95 % CI 1·01, 1·06) for 150-159 g/l, 1·11 (95 % CI 1·05, 1·17) for 160-169 g/l and 1·19 (95 % CI 1·11, 1·27) for ≥170 g/l, respectively. The multivariable-adjusted OR for very PTB (VPTB) was 1·07 (95 % CI 1·03, 1·12) and 1·06 (95 % CI 1·01, 1·12) for women with Hb <110 and ≥150 g/l, compared with those with Hb of 110-149 g/l, respectively. Our study identified a U-shaped relationship between maternal preconception Hb concentration and PTB risk. Both preconception anaemia and high Hb level can significantly increase VPTB risk. Appropriate intervention for women with abnormal Hb levels before pregnancy is very necessary.

Maternal hemoglobin concentrations across pregnancy and maternal and child health: a systematic review and meta‐analysis

“…In total, 272 studies were included in our review and 95 studies met the criteria for inclusion in the meta‐analyses (Fig. ), while the remaining 177 studies are summarized in table format only. A summary of all studies included in the meta‐analyses is provided in Table S2 (online only).…”

“…measured Hb concentrations a median of 5 weeks prior to conception, 1.5 months prior to conception, and on or before the first day of the last menstrual cycle, respectively, while the preconception timing for Maghsoudlou et al . is unclear (1 year before pregnancy) …”

Preconception Hb concentration with risk of spontaneous abortion: a population-based cohort study in over 3·9 million women across rural China

“…This issue is more common in low-income countries, especially in Central and West Africa (48 %) and in South Asia (47 %) (32) . Previous studies have shown that maternal anaemia, especially severe anaemia, can be associated with an increased risk of low birth weight (33,34) , preterm birth (23,35) and smallfor-gestational-age (36) . However, there were only two studies that have assessed the association between maternal anaemia and SA risk.…”

“…A large population-based retrospective cohort study among reproductive-aged (20-49 years) women was conducted based on National Free Pre-pregnancy Check-up Project (NFPCP), which was supported by the National Health Commission and Ministry of Finance of the People's Republic of China, with the purpose to provide free preconception health examinations and follow-up of pregnancy outcomes for reproductive-aged couples who planned to get pregnant within the next 6 months. Published articles detailing the project-related design, organisation and implementation can be found elsewhere (10,23,24) . The current study was conducted according to the guidelines laid down in the Declaration of Helsinki, and all procedures involving humans were approved by the Institutional Research Review Board at the National Research Institute for Health and Family Planning.…”

“…Thus, identifying the association of Hb concentration prior to pregnancy with the risk of SA is much more important to take preconception healthcare and reduce adverse pregnancy outcomes initiated before conception. Previous studies suggested maternal preconception anaemia is associated with increased risk of low birth weight, fetal growth restriction and small-forgestational-age (17,22) , and both preconception anaemia and high Hb concentration can significantly increase the risk of very preterm birth (23) . However, the relationship between preconception anaemia or high Hb concentration and SA risk was not well investigated.…”