Hospital-delivered newborns were enrolled between April 2018 and October 2020 in the Obstetrics and Gynecology Hospital of Fudan University, including a total of 124 newborns with LBW and 393 NBW. Epidemiological data were collected for pregnant women covered maternal age at delivery (<35, ≥35 years), pre-pregnancy body mass index (BMI), maternal education level (no education or primary education, secondary education, higher education), gravidity and parity.
The BMI was calculated by weight before pregnancy /(height2) and grouped into four categories according the China guidelines (underweight, <18.5, normal weight, 18.5-23.9, overweight, 24.0-27.9; obesity, ≥28.0). Preeclampsia was defined as PRH (SBP≥140 mmHg or DBP≥90 mmHg) with proteinuria (24h urinary protein level of >0.3 g or urine dipstick protein level≥+). GDM was diagnosed by oral glucose tolerance test (fasting plasma glucose≥5.1 mmol/L, 1h plasma glucose≥10.0 mmol/L, or 2h plasma glucose≥8.5 mmol/L). The PTB was defined to deliver within 37 weeks of gestation. Gestational age of serum sampling was determined by the result of ultrasound. Serum biochemical parameters were measured within 18 weeks of gestation. Gestational age, delivery mode (eutocia vs. cesarean), gender and birth weight of newborns were obtained from medical records.
Pregnant women were excluded if they were under 18 years old, smoking or drinking, multiple pregnancy, embryo transfer, in vitro fertilization, and microbial infection. Neonates with birth defects, spontaneous abortion, birth weight <1500 g or gestational age <30 weeks were also excluded in this study.
Detection of MTHFR C677T polymorphism
Genomic DNA was extracted from the whole blood of the pregnant women using a column extraction kit. The MTHFR C677T polymorphism was detected by gene chip hybrid analysis following the manufacturer’s instructions. The polymerase chain reaction (PCR), hybridization, gene array detection and analysis were conducted using the BaiO genotype detecting gene array kit and equipment (BaiO Technology Corp., Shanghai). The MTHFR C677T was genotyped as wild (CC), heterozygous (CT) and homozygous (TT) gene type, respectively.
Measurement of biochemical parameters
The biochemical parameters were measured before the 18th week of pregnancy. Plasma hcy was determined using Hitach 7600 automatic chemistry analyzer (Hitach Diagnostics Ltd.). Serum folate, vitamin B12 and vitamin D concentrations were measured using an Architect i2000 Analyzer (Abbott). The cut-off values for distribution of metabolic parameters considered in this study were hyper hcy ≥8μmol/L, folate deficiency <32.5 nmol/L, vitamin B12 deficiency <280 pmol/L, and vitamin D deficiency <30 nmol/L, respectively.
Statistical analyses were performed using the SPSS version 18.0 software (SPSS Inc., Chicago, IL, USA). Variable selection in multivariable modeling was based on clinical and statistical significance. Continuous variables were expressed as mean ± standard deviation (SD) and categorical variables were indicated as number and percent (n, %). Independent-sample t test or chi-square test was used to evaluate the difference in clinical characteristics. A two-sided p-value less than 0.05 was considered to be statistically significant. Multivariable logistic regression analysis was used to determine the adjusted odds ratios (AOR) with 95% confidence intervals (CI) for the associations between folate deficiency and LBW, adjusted for maternal age, pre-pregnancy BMI, MTHFR 677T, PE, delivery mode, parity, and gestational age.