Related Experiment Video

Updated: Oct 4, 2025

Inverse Probability of Treatment Weighting Propensity Score using the Military Health System Data Repository and National Death Index
06:55

Inverse Probability of Treatment Weighting Propensity Score using the Military Health System Data Repository and National Death Index

Published on: January 8, 2020

14.7K

Risk of early birth by body mass index in a propensity score-matched sample: A retrospective cohort study

Rebecca J Baer1,2, Brittany D Chambers2,3, Kimberly Coleman-Phox4

  • 1Department of Pediatrics, University of California San Diego, La Jolla, California, USA.

BJOG : an International Journal of Obstetrics and Gynaecology
|February 8, 2022
PubMed

Insights

Maternal underweight (body mass index [BMI] <18.5 kg/m²) increases the risk of preterm and early term birth. Conversely, higher BMI (≥25.0 kg/m²) is linked to earlier preterm births, though it may decrease the risk of spontaneous preterm birth later in pregnancy.

Area of Science:

  • Reproductive Health
  • Maternal-Fetal Medicine
  • Public Health Nutrition

Background:

  • Body mass index (BMI) is a key indicator of maternal nutritional status.
  • Pregnancy outcomes, including gestational age at birth, can be influenced by pre-pregnancy BMI.
  • Understanding the nuanced relationship between BMI and adverse birth outcomes is crucial for clinical practice and public health initiatives.

Purpose of the Study:

  • To evaluate the association between pre-pregnancy body mass index (BMI) categories and the risk of preterm birth (<37 weeks) or early term birth (37-38 weeks).
  • To investigate these risks within a propensity score-matched cohort to control for confounding maternal factors.

Main Methods:

  • Retrospective cohort analysis of singleton live births in California from 2011-2017.
  • Maternal factors were used to calculate propensity scores for different BMI groups.
  • Exact propensity score matching was employed to create a referent sample (BMI 18.5 to <25.0 kg/m²).
  • Risk ratios (RR) were calculated for preterm and early term birth across various BMI strata.

Main Results:

  • Maternal underweight (BMI <18.5 kg/m²) was associated with an elevated risk of birth between 28-31 weeks (RR 1.2) and 32-36 weeks (RR 1.3), and early term birth (37-38 weeks, RR 1.1).
  • Higher BMI (≥25.0 kg/m²) increased the risk of birth <28 weeks (1.2-1.4 times) but was associated with a reduced risk of birth between 32-36 weeks (RR 0.8-0.9) and 37-38 weeks (RR 0.9).
  • In the propensity score-matched analysis, BMI ≥30.0 kg/m² showed a decreased risk of spontaneous preterm birth with intact membranes between 32-36 weeks.

Conclusions:

  • Maternal underweight is a significant risk factor for both preterm and early term births.
  • Higher maternal BMI (≥25.0 kg/m²) is associated with an increased risk of very early preterm birth (<28 weeks).
  • The relationship between BMI and preterm birth is complex, with higher BMIs potentially reducing the risk of certain types of spontaneous preterm birth later in gestation.
Abstract

Keywords:
body mass indexearlyearly term birthpreterm birthpropensity-matched samplerisk factorspontaneous preterm birth

More Related Videos

External Cephalic Version: Is it an Effective and Safe Procedure?08:49

External Cephalic Version: Is it an Effective and Safe Procedure?

Published on: June 6, 2020

14.8K
Scanning Skeletal Remains for Bone Mineral Density in Forensic Contexts07:56

Scanning Skeletal Remains for Bone Mineral Density in Forensic Contexts

Published on: January 29, 2018

17.8K

Related Concept Videos

Regression Toward the Mean01:52

Regression Toward the Mean

Regression toward the mean (“RTM”) is a phenomenon in which extremely high or low values—for example, and individual’s blood pressure at a particular moment—appear closer to a group’s average upon remeasuring. Although this statistical peculiarity is the result of random error and chance, it has been problematic across various medical, scientific, financial and psychological applications. In particular, RTM, if not taken into account, can interfere when...
6.5K
Bias in Epidemiological Studies01:29

Bias in Epidemiological Studies

Biases can arise at various stages of research, from study design and data collection to analysis and interpretation. Recognizing and addressing these biases is essential to ensure the validity and reliability of epidemiological findings.Broadly speaking, biases in epidemiology fall into three main categories: selection bias, information bias, and confounding. A more detailed description of possible biases is:  
761
Relative Risk01:12

Relative Risk

Relative risk (RR) is a statistical measure commonly used in epidemiology to compare the likelihood of a particular event occurring between two groups. This metric is important for evaluating the relationship between exposure to a specific risk factor and the probability of a particular outcome. It plays a crucial role in medical research, public health studies, and risk assessment. Relative risk quantifies how much more (or less) likely an event is to occur in an exposed group compared to an...
472
z Scores and Area Under the Curve01:17

z Scores and Area Under the Curve

z scores are the standardized values obtained after converting a normal distribution into a standard normal distribution. A z score is measured in units of the standard deviation. The z score tells you how many standard deviations the value x is above (to the right of) or below (to the left of) the mean, μ. Values of x that are larger than the mean have positive z scores, and values of x that are smaller than the mean have negative z scores. If x equals the mean, then x has a z score of...
12.8K
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches01:23

Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches

Biopharmaceutical studies constitute a vital field aiming to enhance drug delivery methods and refine therapeutic approaches, drawing upon diverse interdisciplinary knowledge. In research methodologies, the choice between controlled and non-controlled studies significantly influences the study's reliability and accuracy.
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast,...
190
Hazard Ratio01:12

Hazard Ratio

The hazard ratio (HR) is a widely used measure in clinical trials to compare the risk of events, such as death or disease recurrence, between two groups over time. It reflects the ratio of hazard rates—the instantaneous risk of the event occurring—between a treatment group and a control group. This measure provides valuable insights into the relative effectiveness of a treatment by assessing how the risk of an event differs between the two groups.
For example, in a clinical trial...
280