Poster Presentation Society of Obstetric Medicine of Australia and New Zealand ASM 2015

Background

PTB remains one of the most intractable obstetric issues.

A recent meta-analysis suggests that the presence of thyroid peroxidase antibody (TPO-Ab) significantly increases risk of PTB.

This study was performed to investigate association between TA and TSH at different gestations with and without known thyroid dysfunction and spontaneous PTB.

Method

A retrospective audit was conducted of 1661 thyroid function tests performed on 961 antenatal patients of RWH in 2011. Antibody testing was performed on a small subset (209) of which the majority (68.9%) had hypothyroidism. Exclusion criteria included FDIU, miscarriages, termination or transfer.  789 remaining patients were divided into 735 no thyroid disease and hypothyroid (Group A) and 54 Hyperthyroid (Group B). Group A was further divided into with and without Thyroxine treatment. Only spontaneous labour cases (433/789) were analysed.

Results

The rates of PTB among no thyroid disease, hypothyroid and hyperthyroid patients were 10.0%, 8.6% and 13.2% respectively.  There was no statistically significant correlation between first, second or third trimester TSH with or without treatment (Group A) and gestation at delivery (GAD).

GAD was significantly lower in TPO antibody negative women.  There was no statistically significant difference in GAD between Tg antibody positive and negative women or women positive for both antibodies (Figure 1). 

There was a significant positive correlation between GAD and TSH in Group B (hyperthyroid) in second and third trimesters (Figure 2A & 2B).

Conclusions

Our study of women with spontaneous labour only avoids confounding by inclusion of iatrogenic PTB, a problem of previous studies.  In hyperthyroidism, a significant correlation with GAD suggests that better disease control with higher TSH may prevent spontaneous PTB.

The previously reported association between positive TA and PTB was not observed in this cohort.  Significantly lower GAD was noted in TPO Ab negative women.

We confirmed the previously reported finding of TPO Ab positive women having a significantly higher TSH but only in the first trimester (Table 1).