Thyroid hormone is important for the normal development of a baby during pregnancy. Some studies have shown that even a mildly underactive thyroid (subclinical hypothyroidism) in pregnant women between 11–13 weeks of pregnancy is a risk factor for miscarriage .
Other studies have shown that having high levels of thyroid antibodies in the blood, which are associated with one form of hypothyroidism, during pregnancy can also increase the risk of miscarriage . So, this study tried to screen pregnant women for thyroid function test during early gestation and assess associated factors among pregnant women attending antenatal care clinic at Nekemte Referral Hospital.
According to this finding, based on TSH test, 240(80.0%) of the respondents have normal thyroid stimulating hormone test, 38(12.7%) of the respondents have below normal range TSH test and 22(7.3%) of them have high or above normal TSH test. Two subjects have TSH above 10µIU/ml. A total of 86.7% of pregnant woman (492/573) showed normal thyroid function tests. This is in line with study done in Turkey .
In line with TSH test, the test of FT4 conducted and in 53(17.7%) of the cases the test was normal and majority 247(82.3%) of the subjects have high T4 test results. In addition to this 31(10.3%) of the study subjects have suppressed TSH level and increased FT4 levels at the earlier age of the pregnancy. On other hand 236 (78.7%) of the study subjects have above normal T3 test result and 64(21.3%) of the remaining were fall in normal range of the test result. And also 210(70.0%) of the study subjects were observed with both T3 and T4 test raised above normal range. This is different from study done in Sudan . The possible difference is may be because of nutritional status difference, geographical location multiple pregnancy, birth interval and previous bleeding history which is not the case in current study.
Accordingly, OH can be defined as TSH concentration > 2.5 µIU/ml and FT4 concentration below normal range. In maternal Subclinical Hypothyroidism (SCH), patient may not have symptoms but, the concentration of TSH is above 2.5 µIU/ml with normal FT4 concentrations. This is in contrast with previous study in which the average ranges of TSH and T4 were (0.5–6.5 mIU/L) and T4 (10.5–20.4 Pmol/L) respectively and Subclinical and overt hypothyroidism was found in 56 (13.7%) of women . This difference might be due to study site and study population difference.
Among the study subjects, 14(4.7%) have Subclinical Hypothyroidism (SCH) and one (0.3%) subject has overt hypothyroidism. This is comparable with other study, in which the prevalence of thyroid dysfunction in pregnancy was 10.8% with hypothyroidism being 9.2%, out of which 8.5% were cases of subclinical hypothyroidism and 0.7% was cases of overt hypothyroidism . But in contrast with previous study done elsewhere in which (10.5%) had subclinical hypothyroidism, 3.2% had overt hypothyroidism  and 0.5% had hypothyroidism, 8.9% had subclinical hypothyroidism, and 2.8% had hyperthyroidism  and the prevalence of hypothyroidism and hyperthyroidism was 12 and 1.25%, respectively . This difference might be due to difference in study site and study population.
In the present study, among the study subjects, 6(2%) of them had subclinical hyperthyroidism and 3(1%) of the subjects were develop overt hyperthyroidism. Only one subject found with TSH level > 2.5 µIU/ml and FT4 less than normal range. Of the study groups one (0.3%) of them has overt hyperthyroidism. This is contrast with other study done elsewhere; in which 260 pregnant women (19.41%) had TSH values more than 3.0 mIU/L and of these, 216 had normal T4 value, hence labeled as subclinical hypothyroidism and 44 had low T4, hence termed overt hypothyroidism. Three pregnant women had overt hyperthyroidism and 11 had subclinical hyperthyroidism. Nine women had low T4 values-Isolated hypothyroidism  and also forty-three women (10.5%) had subclinical hypothyroidism, thirteen (3.2%) had overt hypothyroidism . This difference might be due to study population and study area difference. Different factors have been assessed for association with hypothyroidism in multivariate logistic regression. Factor showed association with hypothyroidism during pregnancy were spouse occupation, pregnant women whose Husband occupation was government employee were 10% less likely to develop hypothyroidism this is probability related to consumption of food rich in iodine content. But there were no similar studies done elsewhere which indicated the significance of these factors with hypothyroidism and hyperthyroidism to compare with the present study.
Other variable which shown association with hypothyroidism was presence of radio in house, those pregnant women who has Radio in the household were 20% less likely to develop hypothyroidism. This is may be related to awareness of the family as radio can be source of information on consuming iodine rich food and utilization of iodized salt in household level. Presence of television also shown association in multivariate, pregnant women who has television in their house were 30% less likely to develop hypothyroidism. This is also related to information announced on television is more familiar and practical focus for pregnant women easily understand practice on iodine utilization. However, there were no similar studies done elsewhere which indicated the significance of these factors with hypothyroidism and hyperthyroidism to compare with the present study.
On other hand pregnant women who would not treat drinking water at household level were 2.4 times more likely to develop hypothyroidism than those who treat water for drinking. This is may be related to some infectious diseases that may have effect on iodine utilization and also some infectious diseases may cause thyroid diseases disorder. This was not the case in the previous study done showed significant association between overt hypothyroidism and history of infertility, history of miscarriage, stillbirth, preterm deliveries, BMI, maternal age and iodine deficiency [21, 22]. But in the present study, marital status, religion, ethnic group, education level, occupation of respondent, family size and age of respondent were not show an association with hypothyroidism. But there were no similar studies done elsewhere to compare with.
Strength And Limitation Of The Study
The strength of this study is its inclusion of early age pregnancy and laboratory-based study was conducted. The limitation of this study was its cross sectional design effect and urine iodine test was not done.