Impact of Adolescent Pregnancy on Bone Density in Underprivileged Pre-Menopausal Indian Women

High prevalence (31.5%) of adolescent pregnancies (AP) have been reported in India. Reports suggest that pregnancy during adolescence may have deleterious effects on peak bone mass. Very few studies have described the long-term effects of a history of AP on bone mass. The objective of this study was to compare bone mineral density (BMD) and bone geometry of premenopausal women with first childbirth during adolescence (i.e., before age of 19 years) or after 20 years. A cross-sectional study was conducted in 242 women (age 28.0-54.5 years) from Pune, India (November, 2015 to November, 2017). Women were divided into 2-groups: Group-1: women-who had 1st-pregnancy and childbirth before 19 years of age (AP n = 131) and Group-2: women-who had 1st pregnancy after 20 years of age (non-AP n = 111). Demographic data, anthropometric measurements, and biochemical tests were performed using standard protocols. Physical activity and nutrient intakes were recorded using validated questionnaires. Areal BMD and bone geometry were measured using Dual-Energy-Absorptiometry-DXA (Lunar-iDXA, GE Healthcare) and peripheral-quantitative-computed-tomography-pQCT (XCT2000, Stratec Inc.). Mean age of the study group was 37 ± 4.6 years; in women from group-1 mean age at first delivery was 16.9 ± 1.6 years as against 22.6 ± 3.1 years in group-2. Both groups were similar in body mass index and socioeconomic status. pQCT measured radial diaphyseal cortical thickness (1.97 ± 0.3 mm vs 1.88 ± 0.3 mm resp., p = 0.016, periosteal circumference (38.0 ± 3.6 mm vs 36.7 ± 2.5 mm, resp. p = 0.016), total bone area (114.3 ± 24.8 mm² vs 108.7 ± 14.7 mm² resp. p = 0.026) and stress-strain index (SSI = 217 ± 75 vs 201 ± 40 mm³ resp. p = 0.042) were significantly higher in group-1 than group-2. After adjusting for anthropometric and lifestyle parameters, pQCT measured cortical thickness (1.98 ± 0.03 mm in group-1, 1.87 ± 0.03 mm group-2, p = 0.01, mean ± SE) and iDXA derived aBMD at forearm were still significantly higher (0.599 ± 0.006 g/cm3 vs 0.580 ± 0.006 g/cm3, p = 0.023) in Group-1. Our data suggest that women with a history of adolescent pregnancy had better bone geometry and higher aBMD at radius in later years. We speculate that early exposure to pregnancy resulted in higher aBMD at the radius and induced changes at radial diaphysis with bones becoming thicker and wider among these women.