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. 2022 Feb 11;22(1):121.
doi: 10.1186/s12884-022-04418-3.

Severity of low pre-pregnancy body mass index and perinatal outcomes: the Japan Environment and Children's Study

Kentaro Nakanishi  1 , Yasuaki Saijo  2 , Eiji Yoshioka  3 , Yukihiro Sato  3 , Yasuhito Kato  1   3 , Ken Nagaya  4 , Satoru Takahashi  5 , Yoshiya Ito  6 , Sumitaka Kobayashi  7 , Chihiro Miyashita  7 , Atsuko Ikeda-Araki  7   8 , Reiko Kishi  7 ; Japan Environment and Children’s Study (JECS) Group
Collaborators, Affiliations

Severity of low pre-pregnancy body mass index and perinatal outcomes: the Japan Environment and Children's Study

Kentaro Nakanishi et al. BMC Pregnancy Childbirth. .

Abstract

Background: The extremes of maternal pre-pregnancy body mass index (BMI) are known to be risk factors associated with obstetric and adverse perinatal outcomes. Among Japanese women aged 20 years or older, the prevalence of underweight (BMI < 18.5 kg/m2) was 11.5% in 2019. Maternal thinness is a health problem caused by the desire to become slim. This study aimed to investigate the association between the severity of maternal low pre-pregnancy BMI and adverse perinatal outcomes, including preterm birth (PTB), low birth weight (LBW), and small-for-gestational age (SGA).

Methods: We conducted a prospective cohort study using data from the Japan Environment and Children's Study, which recruited pregnant individuals between 2011 and 2014. Pre-pregnancy BMI was categorized as severe-moderate underweight (BMI < 16.9 kg/m2), mild underweight (BMI, 17.0-18.4 kg/m2), low-normal weight (BMI, 18.5-19.9 kg/m2), high-normal weight (BMI, 20.0-22.9 kg/m2), overweight (BMI, 23.0-24.9 kg/m2), and obese (BMI ≥ 25.0 kg/m2). The high-normal weight group was used as the reference for statistical analyses. Adjusted logistic regression was performed to evaluate the association between pre-pregnancy BMI and PTB, LBW, and SGA.

Results: Of 92,260 singleton pregnant individuals, the prevalence was 2.7% for severe-moderate underweight, 12.9% for mild underweight, and 24.5% for low-normal weight. The prevalence of adverse outcomes was 4.6% for PTB, 8.1% for LBW, and 7.6% for SGA. The adjusted odds ratios (aORs) for PTB were 1.72 (95% confidence interval [CI], 1.46-2.03) for severe-moderate underweight and 1.26 (95% CI, 1.14-1.39) for mild underweight. The aORs of LBW were 2.55 (95% CI, 2.27-2.86) for severe-moderate underweight, 1.64 (95% CI, 1.53-1.76) for mild underweight, and 1.23 (95% CI, 1.16-1.31) for low-normal weight. The aORs of SGA were 2.53 (95% CI, 2.25-2.84) for severe-moderate underweight, 1.66 (95% CI, 1.55-1.79) for mild underweight, and 1.29 (95% CI, 1.21-1.38) for low-normal weight.

Conclusions: A dose-response relationship was found between the severity of low pre-pregnancy BMI and PTB, LBW, and SGA. Even low-normal BMI (18.5-19.9 kg/m2) increased the risk of LBW and SGA. This study provides useful information for pre-conception counseling in lean individuals.

Keywords: Adverse perinatal outcomes; Low birth weight; Maternal body mass index; Preterm birth; Small-for-gestational age.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Flow diagram of the study participants
Fig. 2
Fig. 2
Maternal pre-pregnancy BMI and the risk of adverse perinatal outcomes using restricted cubic spline. Values are adjusted odds ratio and 95% confidence interval compared with the referent group (high-normal weight, 20.0–22.4 kg/m2), adjusted for maternal age at delivery, parity (except for small-for-gestational age [SGA] analysis), assisted reproductive technology, maternal smoking status, maternal alcohol consumption, maternal educational background, history of preterm birth, and the medical history of hypertension, diabetes mellitus, autoimmune disease, and thyroid disease. The adjusted odds ratios are shown as solid lines. The 95% confidence interval is indicated by dotted lines. A PTB: preterm delivery before 37 weeks of gestation. B VPTB: preterm delivery before 34 weeks of gestation. C LBW: low birth weight D VLBW: very low birth weight. E ELBW: extremely low birth weight. F SGA: small-for-gestational age. BMI, body mass index
See this image and copyright information in PMC

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