Changes in maternal abdominal subcutaneous fat layers using ultrasound: A longitudinal study

Abdominal adiposity and subcutaneous fat (SF), an important endocrine organ for health outcomes, can be divided into two layers, superficial (SSAT) and deep subcutaneous adipose tissue (DSAT) each with a different histological and metabolic function. The aim was to investigate longitudinal changes in maternal abdominal SF thickness and its layers throughout pregnancy and post-partum within body mass index (BMI) categories.

A prospective longitudinal study of 214 women was performed measuring abdominal SF using ultrasound at 12-14(M1), 18-20(M2), 26-29(M3) and 33-36 weeks' gestation (M4) and 6-8 weeks post-partum. SF thickness (SFT), SSAT and DSAT were measured. A ratio of DSAT/SSAT (D/S) was calculated. Measurements were compared to baseline and BMI evaluating for interaction with changes over time.

Of the 214 women, 43.5%(93) were normal weight, 25.7%(55) overweight and 30.8%(66) obese. SFT and SSAT decreased from M1 to M4 for the overweight and obese whilst remaining stable for normal weight women. For all BMI categories SFT and SSAT increased post-partum. DSAT decreased significantly in the obese and overweight and increased significantly in the normal weight. Obese women had a higher D/S at M1 that decreased at M2 and remained constant to post-partum. D/S increased at M2 then decreased in the overweight. Normal weight women increased D/S at M2-M4.

The results indicate a difference in distribution and mobilisation of fat in SSAT, and DSAT abdominal subcutaneous compartments within the different BMI categories in pregnancy. Understanding how fat mobilises during pregnancy may be fundamental to understanding obesity related complications.