PREDICTION OF POST-PARTUM THYROID-DYSFUNCTION - CAN IT BE IMPROVED

Background: Screening pregnant women for thyroid peroxidase antibodies (TPOAb) to identify those at risk for post partum thyroid dysfunction (PPTD) is controversial, mainly because of the low positive predictiv e value (ppv) of TPOAb. Objectives: To evaluate if the ppv of TPOAb ca n be enhanced, either by taking into account the time of TPOAb, testin g, or by combining this parameter with other putative determinants of PPTD such as smoking, family history or other autoimmune diseases. Met hods: A prospective study was performed in the Kempenland region (sout heastern Netherlands). Three hundred and ten unselected women were vis ited at 12 and 32 weeks gestation and 4, 12, 20, 28 and 36 weeks post partum. Serial thyroid stimulating hormone (TSH), free thyroxine (fT(4 )) and TPOAb testing was performed. Thyroid dysfunction (TD) was defin ed as abnormal TSH either in combination with abnormal fT(4) (overt TD ) or without abnormal fT(4) (subclinical TD). PPTD was defined as over t TD post partum. Multivariate regression analysis was performed for d etermining independent risk factors for PPTD, The sensitivity and spec ificity of TPOAb at different time points and at different concentrati ons were calculated and presented in receiver operating characteristic (ROC) curves. Women who had experienced PPTD were followed for 2.5-3 years. Results: Data from 291 women were available for analysis. Serum fl; declined during pregnancy and returned to baseline values post pa rtum. TD in gestation was present in 23 women (7.9%): serum TSH was tr ansiently decreased in 13 (6 had overt gestational thyrotoxicosis (2.1 %)) and increased in 10 (2 had TPOAb). Both point prevalence and conce ntration of TPOAb decreased during gestation and returned to baseline levels within 12 weeks post partum. TD in post partum was present in 3 6 women (12.4%): 21 had subclinical and 15 overt TD. Out of the 15 wom en with overt TD (incidence of PPTD: 5.2%) 10 were positive for TPOAb (TPOAb+); 9 had thyrotoxicosis (4 TPOAb+), 5 hypothyroidism (5 TPOAb+) and 1 thyrotoxicosis followed by hypothyroidism (TPOAb+). Independent risk factors for PPTD were TPOAb (relative risk (RR)= 27.2), bottle f eeding (RR = 11.1) and smoking habits (ever smoked: RR= 3.1: women wit h PPTD had smoked more cigarettes for a longer period of time). The se nsitivity of TPOAb testing was highest at 12 weeks gestation (0.67). T he ppv of TPOAb was 0.31-0.75 (depending on time of testing and concen tration), increasing slightly to 0.38-0.80 when combined with bottle f eeding or smoking habits. There appeared to be an autoimmune form of P PTD in 2/3 of cases and a nonautoimmune form; women with the autoimmun e form were at risk for developing permanent hypothyroidism. Conclusio ns: A maximum of 2/3 of PPTD cases can be predicted from the presence of TPOAb because 1/3 remained negative for TPOAb. The most appropriate time for TPOAb testing is in the first trimester of pregnancy. The co mbination of TPOAb testing with anamnestic determinants of PPTD does n ot increase ppv substantially.