Levels of cord blood thyroid stimulating hormone after external cephalic version

Abstract

Objective To investigate the relationship between breech presentation, external cephalic version and levels of cord blood thyroid stimulating hormone.

Design Case–control study.

Setting University teaching hospital.

Population The study group consisted of 289 consecutive singleton deliveries at term over a four-year period, all of whom had an attempt at external cephalic version performed near term for breech presentation. The control group included 23,001 singleton term deliveries during the same four-year period.

Methods Between group differences were compared with the Mann-Whitney U test or χ² test when appropriate.

Main outcome measures Levels of cord blood thyroid stimulating hormone and the incidence of false positive screening results for congenital hypothyroidism.

Results Babies who were born vaginally after prior successful external cephalic version had significantly higher median levels of cord blood thyroid stimulating hormone (6.4 vs 6.0mIU/L, P=0.034) and the incidence of false positive screening for thyroid stimulating hormone (12.9% vs 7.2%, P=0.016, OR 1.9) compared with babies with spontaneous cephalic presentation. In babies with a breech presentation born by elective caesarean section, previous attempts at external cephalic version had no effect on cord blood thyroid stimulating hormone levels. There was also no difference in the levels of cord blood thyroid stimulating hormone between cephalic and breech-presenting fetuses born by elective caesarean section. However, breech-presenting babies born by emergency caesarean section after onset of labour had higher median levels of cord thyroid stimulating hormone than those with cephalic presentation (5.1 vs 4.5 mIU/L, P=0.008).

Conclusion Levels of cord blood thyroid stimulating hormone are elevated in babies born vaginally after a successful external cephalic version. This finding may represent a biological difference in fetal response to the stress of labour in breech-presenting fetuses, which is not correctable by a successful external cephalic version.