The 2009 Institute of Medicine (IOM) publication established guidelines for gestational weight gain goals based on the maternal pre-pregnancy body mass index (BMI) classification. Afterward, domestic scholars conducted studies to research whether pre-pregnancy BMI and gestational weight gain (GWG) were related to pregnancy outcomes [1]. Guidelines for Pre-Conception and Pregnatal Care (2018) categorized BMI and proposed a corresponding range of total GWG based on different pre-pregnancy BMI. However, it did not specify the appropriate ranges of the rates of GWG in the first, second and third trimester, respectively. Previous studies [2, 3, 4] regarding pregnancy outcomes were limited by the use of either total GWG or GWG in a specific period and did not observe the influence of the dynamic change of GWGr on adverse outcomes. To figure out whether timely adjustment of GWGr could affect maternal and infant outcomes, a retrospective analysis was performed in this study according to clinical data of 6235 singleton pregnancies with normal pre-pregnancy BMI at two medical centers.

We conducted a retrospective cohort study of singleton pregnant Chinese women using electronic medical record data from the First Affiliated Hospital of Soochow University and the Fifth People’s Hospital of Wujiang District. Those with a history of chronic hypertension, diabetes, cardiovascular disease, high or low BMI before pregnancy were excluded from the study. We additionally excluded mothers who received assisted reproductive techniques or delivered stillbirth or malformed infants.

The adequacy rates of GWG were defined according to the 2009 IOM recommendations as gaining 0.04~0.17 kg per week in the first trimester and gaining 0.35~0.50 kg per week in the second and third trimesters. Maternal weight before gestation, at 13 weeks and 28 weeks of gestation and before delivery were recorded to calculate GWG in the first trimester (weight at 13 weeks gestation—pre-pregnancy weight), second trimester (weight at 28 weeks gestation—13 weeks gestation), and third trimester (weight before delivery—28 weeks gestation). Finally, the trimester-specific rates of GWG could be calculated by dividing the GWG by the corresponding number of weeks.

The rate of gestational weight gain in the first trimester was defined in this study as “GWGr-1”, similarly, the rate of gestational weight gain in the second trimester was defined as “GWGr-2” and the rate of gestational weight gain in the third trimester was defined as “GWGr-3”. In addition, the rate of gestational weight gain in the second and third trimesters was defined as “late GWGr”.

Pregnancy outcomes were categorized into maternal and neonatal outcomes. Maternal outcomes included cesarean section (CS), post-partum hemorrhage, obstructed and prolonged labor, gestational diabetes mellitus (GDM) and hypertensive disorders of pregnancy (HDP), and neonatal outcomes included preterm delivery, large for gestational age (LGA) and small for gestational age (SGA).

Multivariable logistic regression was conducted to calculate odds ratios (ORs) and 95% confidence intervals (CIs) evaluating the association between trimester-specific GWGr and risk of CS, post-partum hemorrhage, obstructed and prolonged labor, GDM, HDP, preterm delivery, LGA and SGA. The measurement data is expressed as mean and standard deviation (SD) and enumeration data is expressed in percentage. All analyses used SPSS 19.0 statistical software (IBM Corp., Chicago, IL, USA) with statistical significance defined as p 0.05.

For the 6235 women included in this study, 4046 and 1043 had GWGr-1 above and below the IOM guidelines. Of the women with adequate GWGr-1, 424 and 56 gained above and below the guidelines in the second trimester. Overall, there were 666 women with adequate rates of weight gain in each trimester during pregnancy.

In this analysis of 6235 singleton pregnancies, we found associations between adjusting GWGr and several adverse maternal and neonatal outcomes including CS, HDP, GDM, postpartum hemorrhage, obstruction and prolongation of labor, LGA, SGA and preterm delivery. In general, decreasing the GWGr in the second and third trimesters when the GWGr in the first trimester was inappropriate or adjusting GWGr-3 after gaining improper weight in the second trimester would contribute to a varying degree of improved pregnancy outcomes.

For neonatal birth weight, as long as GWGr-1 was inappropriate, regardless of whether it was excessive or inadequate, maternal late GWGr above the IOM recommendation was associated with a higher risk of LGA. The results were in line with a prospective cohort analysis which consisted of 14,219 Chinese rural nulliparous women [5], suggesting patients with late GWGr in the highest quintile had higher risks of macrosomia (adjusted OR = 1.89, 95% CI: 1.46~2.45) and LGA (adjusted OR = 1.56, 95% CI: 1.31~1.85) compared with those in the middle quintile. In addition, studies among American and Brazilian women were also consistent with our results [6, 7]. All the above shows that timely adjustment of late GWGr to the appropriate range was beneficial to neonatal outcomes.

Of note, women with appropriate GWGr-1 in this study were not associated with LGA, SGA or preterm delivery no matter how variable the GWG in the second and third trimesters, indicating that proper preemptive management of early weight gain was necessary to reduce the risk of developing adverse neonatal outcomes. This was also confirmed by a retrospective study conducted in Korea [8].

Earlier prevention and diagnosis of adverse pregnancy complications such as HDP is important for pregnancy. Our study shows women with inadequate GWGr-1 had higher odds of HDP when their late GWGr was excessive, and so did women with appropriate GWGr-1 and excessive GWGr-2 and GWGr-3. The former underwent a rapid increase from GWGr-1 to late GWGr and the GWGr of the latter increased rapidly from the first trimester to the second trimester. However, patients whose GWGr-1 and late GWGr were both excessive were not associated with HDP, and women with excessive GWGr-1 would have lower odds of HDP if they underwent strict weight control in mid and late pregnancy. The reason for this discrepancy might be the rapid increase of GWGr. Compared to the women with higher risk of HDP, the latter has a decrease or a more substantial increase of GWGr. Therefore, avoiding the uncontrolled rapid increase of weight gain rate might be an effective way to prevent HDP.

Our results also indicated that GWGr in late pregnancy was closely related to CS. We found a higher risk of CS in women with excessive late GWGr regardless of GWGr-1 and in patients with excessive GWGr-3 no matter of GWGr-2, suggesting that prompt control of GWGr even during the third trimester was beneficial to improving pregnancy outcomes.

We acknowledge several limitations to this study. We investigated singleton pregnant women at two medical centers but most of them were from urban areas, thus they may not represent the entire population in Chinese women. Besides, apart from gestational weight, abnormalities of macronutrients, vitamins, and trace elements during pregnancy are closely related to adverse pregnancy outcomes [9]. For example, blood lipid during pregnancy is related to GDM, HDP and intrahepatic cholestasis of pregnancy (ICP) [10]. In addition, Iron deficiency correlates with low birth weight infants and can increase the risk of intrauterine growth retardation and neonatal nutrition neurodevelopmental disorder [11, 12]. Moreover, calcium supplementation during pregnancy can also prevent preterm birth, HDP and GDM [13, 14, 15]. However, information regarding the dietary structure and lifestyle during pregnancy was not available in our medical records. To fully understand the impact of GWG and GWGr on pregnant women and their offspring, prospective studies are warranted to follow up to specify appropriate ranges of the rates of GWG applicable in the clinical populations.

Timely adjustment of GWGr could improve both maternal and neonatal outcomes, therefore, it is critical to managing the rate of gestational weight gain, even during late pregnancy.

Conceptualization—BH; data curation and writing - original draft preparation—HC and HZ; supervision—BH, YC and LZ. All authors have read and agreed to the published version of the manuscript.

The study was approved by the Ethics Committee of the First Affiliated Hospital of Suzhou University (protocol code No. 107 and date of approval June 3rd, 2020). Written informed consent was obtained from the individuals.

We would like to express our gratitude to all the staff at the First Affiliated Hospital of Soochow University and the Fifth People’s Hospital of Wujiang District who helped us in conducting this research. Thanks to all the peer reviewers for their opinions and suggestions.

This research was funded by the Jiangsu Commission of Health (No. H2019010).

The authors declare no conflict of interest.