British Journal zyxwvutsrq of Obsieirics zyxwvutsrq and Gynaecology October zyxwvutsrq 1989, Vol. zyxwvuts 96, zyxwvutsrq pp. 1224-1227 Neonatal thyrotrophin and mode of delivery T. T. LAO, N. S. PANESAR Summary. This study was performed to assess the association between labour and the mode of delivery with the umbilical cord plasma thyrox- ine (T4) and thyroid-stimulating hormone (TSH) concentrations in full- term uncomplicated pregnancies delivered in our hospital. Babies born vaginally had statistically significantly higher umbilical cord plasma TSH but similar T4 concentrations than babies born by caesarean section. Labour was not associated with either higher TSH or T4 concentrations. All the babies with an elevated TSH concentration (>20 m i d ) were born vaginally. Our findings indicate that the mode of delivery should be taken into consideration in the interpretation of umbilical cord plasma TSW results. Screening for congenital hypothyroidism by measuring umbilical cord plasma thyroxine (T4) and thyroid-stimulating hormone (TSH) has now become an established practice (Fisher et al. 1979; John 1987). Because of the relatively wide range of T4 concentrations in the umbilical cord plasma, TSH has been suggested as a more reliable index variable (Walfish 1976). Whereas the diagnosis is easy if an elevated TSH con- centration is associated with a low T4 con- centration, it is less certain if the latter is normal, as the TSH concentration may return to normal after a few weeks, or increase further with a fallingT4 concentration (John 1987). Our recent study (Lao & Panesar 1989) examining the association between mode of delivery and cor- tisol concentrations in cord blood revealed higher concentrations in babies born vaginally. In the same light we wondered if the stress of labour and delivery would be associated with an elevation of TSH concentration in addition to the TSH surge which is a common phenomenon Prince of Wales Hospital, Shatin, Hong Kong Department of Obstetrics and Gynaecology T. T. LAO Senior Lecturer Department zyxwvutsr of Chemical Pathology N. S. PANESAR Lecliirer Correspondence: Dr T. T. Lao 1224 in newborn infants. The present study was con- ducted to look at the relation between the mode of delivery and the cord blood T4 and TSH con- centrations, which are now routinely measured for every baby born in our hospital as the screen- ing test for congenital hypothyroidism. Patients and methods In a retrospective survey, four groups of babies born during a 2-month period were selected according to the mode of delivery. The first group (A) comprised those who had a normal spontaneous vaginal birth zyx (n = 59) of whom 30 (51%) were born after the mother had received epidural analgesia in labour; the second group (B) comprised babies born by forceps for indica- tions other than fetal distress (n = 31); the third group (C) comprised those who had been born by elective caesarean section (n = 43); and the last group (D) included babies born by emer- gency caesarean section after their mother failed to progress in labour (n = 48). All the babies were singletons and had been born at term with- out any complications, such as neonatal asphyxia, birth trauma or congenital malforma- tions. The mothers did not have any obstetric or medical complications. The exclusion of babies associated with obstetric, medical and perinatal complications should remove other possible