Influences of perinatal factors on cord blood thyroid-stimulating hormone level

BACKGROUND

Cord blood thyroid-stimulating hormone level is affected by various perinatal factors. The aim of this study is to investigate the relative impact of these factors on the cord blood thyroid-stimulating hormone results in singleton pregnancies.

METHODS

The study group consisted of 20,086 consecutive singleton deliveries over a 3 year period. The effect of mode of delivery, infant sex, gestation at birth, birth weight, and duration of labor on the incidence of false elevation of cord blood thyroid-stimulating hormone was assessed by univariate analysis and logistic regression.

RESULTS

There was an independent positive association between false elevation of cord blood thyroid-stimulating hormone (> or =15.0 mIU/L) and birth weight (p=0.005), male infant sex (p<0.001), and instrumental delivery (p<0.001). Both elective and emergency cesarean section were negatively associated with elevated cord thyroid-stimulating hormone level (p<0.001). When the cutoff level was raised to 40.0 mIU/L, none of the variables examined were significant. The incidence of false positive tests (> or =15.0 mIU/L) was higher in neonates born by cesarean section for failed instrumental delivery and fetal distress than for failure to progress of labor (34.7% vs 4.5% vs 1.3% respectively, p<0.001).

CONCLUSIONS

While the incidence of false positive screening was significantly affected by various perinatal factors when the thyroid-stimulating hormone cutoff level is low, it was unaffected at a high cutoff level. The present study also provides further evidence that cord blood thyroid-stimulating hormone level reflects fetal response to perinatal stress events.

Levels of cord blood thyroid stimulating hormone after external cephalic version

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 chi2 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 6.0 mlU/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.