Introduction: A breech presentation occurs in 35% of all full-term pregnancies and is associated with increased risk of maternal and foetal morbidity. Factors known to increase the risk of breech presentation include prematurity, low birth weight and multiple pregnancies. Recent studies suggest maternal thyroid hormone deficiency in late pregnancy may also be a risk factor. Our study aims to assess if a breech presentation at 36 weeks gestation in a healthy singleton cohort is associated with maternal thyroid hormone deficiency or thyroid autoimmunity.
Methods: Serum blood samples obtained during routine clinical care from 285 women, with no known thyroid disease and a singleton breech or cephalic pregnancy at 3638 weeks gestation, were analysed for thyroid function tests (TSH and FT4) and TPO antibodies by the local NHS pathology department. Prevalence of subclinical hypothyroidism (defined as serum TSH above 2.5 mlU/l), maternal hypothyroxinaemia (defined by FT4 below the trimester specific reference range and TSH 2.5 mIU/l or less) and thyroid autoimmunity (defined as titre of TPO antibodies >34 IU/l) was determined in women with breech and cephalic presentations for comparison.
Results: When comparing breech (n=147) with cephalic (n=138) presentation there was no difference in maternal age (mean (S.D.)- 30.6 (5.1) vs 31.4 (5.30) years, P=0.3), BMI at booking (median(IQR)-23.8 (2734) vs 25 (2835) kg/m2, P=0.09) or rates (%) of: primiparous pregnancies (43.2 vs 38.7, P=0.45), smoking (13.5 vs 6.6, P=0.06),or multivitamin use (40.8 vs 39.9). There was no difference in the prevalence of subclinical hypothyroidism (27.2 vs 26.8%, P=0.94), maternal hypothyroxinaemia (5.4 vs 2.9%, P=0.29) or positive TPO antibodies (6.2 vs 5.1%, P=0.69)
Conclusion: A breech presentation at 36 weeks gestation in a healthy singleton cohort is not associated with known markers of maternal hypothyroidism or thyroid autoimmunity.