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. 2020 Nov;23(16):2963-2972.
doi: 10.1017/S1368980019003811. Epub 2020 Mar 5.

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

Qin Xu  1   2 , Ying Yang  2   3 , Fangchao Liu  4 , Long Wang  5 , Qiaomei Wang  6 , Haiping Shen  6 , Zongyu Xu  6 , Yiping Zhang  6 , Donghai Yan  6 , Yuan He  2   3 , Ya Zhang  2   3 , Hongguang Zhang  2   3 , Zuoqi Peng  2   3 , Xu Ma  2   3   4
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Preconception Hb concentration with risk of spontaneous abortion: a population-based cohort study in over 3·9 million women across rural China

Qin Xu et al. Public Health Nutr. 2020 Nov.

Abstract

Objective: Evidence on the relationship between maternal Hb concentration and spontaneous abortion (SA) risk is limited and conflicting. The purpose of the study was to evaluate whether maternal preconception anaemia or high Hb concentration is associated with risk of SA.

Design: A population-based cohort study established between 2013 and 2017.

Settings: Local maternal and child care service centres in each county.

Participants: In total, 3 971 428 women aged 20-49 years, who participated in National Free Pre-Pregnancy Checkups Project from 2013 to 2016 and successfully got pregnant before 2017 in rural China.

Results: A total of 101 700 (2·56 %) women were recorded having SA, with highest SA rate in women with severe anaemia (4·58 %). Compared with women with Hb of 110-149 g/l, the multivariable-adjusted OR for SA was 1·52 (95 % CI: 1·25, 1·86) for women with Hb < 70 g/l, 0·92 (0·84, 1·01) for 70-99 g/l, 0·80 (0·77, 0·83) for 100-109 g/l, 1·11 (1·08, 1·15) for 150-159 g/l, 1·12 (1·04, 1·20) for 160-169 g/l and 1·02 (0·93, 1·12) for ≥ 170 g/l, respectively. An approximate U-shaped curve for the risk of SA with Hb concentrations was observed when Hb concentrations less than 145 g/l, above which the association plateaued (Pnon-linear < 0·001).

Conclusions: Severe anaemia and high Hb concentration before pregnancy were associated with an increased risk of SA. Women with mild anaemia prior to pregnancy had lower risk of SA. Underlying mechanisms need to be further studied.

Keywords: Anaemia; Cohort study; High Hb; Pre-pregnancy; Spontaneous abortion.

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Figures

Fig. 1
Fig. 1
Flowchart of the participants. *Sexually transmitted disease including infection of gonorrhoea, syphilis and chlamydia
Fig. 2
Fig. 2
Dose–response relationship between maternal preconception Hb concentrations and the risk of spontaneous abortion. Graphs show the crude (a) and multivariable-adjusted (b) predicted ORs of associations between maternal preconception Hb concentrations and the risk of spontaneous abortion, respectively. In the graph, black lines and shaded grey areas represent predicted ORs and 95 % CIs, respectively. Study participants with the highest 0·1 % of Hb (3945 women, >195 g/l) were excluded to minimise the potential impact of outliers. Covariates in the multivariable-adjusted model included variables in Model C from Table 2
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