recruited between October 1993 and December 1994 and gave their informed consent to participate in the study. Seventy-four women (17.0 %) had a body mass index (BMI; in kg/m2) >25 and 54 women (12.6%) had a BMI >26 before becoming pregnant (Table 1). Also shown in Table 1 is the frequency of obesity among pregnant women or women of childbearing age in different cohorts in which relative weight before pregnancy was reported (1–8).
OUTCOME OF PREGNANCY IN OVERWEIGHT WOMEN: DIFFERENCES IN STUDY DESIGNS Pregnancy outcome in overweight mothers was addressed as early as 1945 (9). Since then, study designs have varied widely (1, 3, 10–20). Differences in types of studies, thresholds used to define overweight, and definitions of control patients can result in major discrepancies in the data provided. Shown in Table 2 are some differences in definitions of overweight and choices of control groups in studies addressing the outcome of pregnancy in overweight women published since 1945. Other important differences include the time and length of the study period, the choice of exclusion criteria (eg, previous maternal pathology, multiple pregnancies, and stillbirths), and the characteristics of the population studied (eg, age, ethnic origin, and social background). Therefore, although most authors agree that pregravid overweight increases maternal and fetal morbidity, detailed comparisons between reports may be hazardous, and for some complications, rates vary within a broad range.
MATERNAL MORBIDITY
Carbohydrate intolerance
Overweight is a risk factor for impairment of carbohydrate tolerance both in the nonpregnant state and during pregnancy. Fasting and postabsorptive plasma insulin concentrations are higher in obese pregnant women than in nonobese pregnant women (21). However, insulin secretion is increased enough in many obese women to maintain normoglycemia. Conversely, approximately