HYPOTHYROIDISM IN PREGNANCY
Thyroid disease is particularly common in women of child-bearing age. As aresult, one should not be surprised that thyroid disease can be complicate the course of pregancyTi is roughly estimated that 2.5% of all pregnant women have some degree of subclinical hypothyroidism . however , the pravalence may change according to ethnicity and geographical variation To understand the relationship between hypothyroidism and pregnancy, it is necessary to first understand the endocrinology of pregnancy. Pregnancy triggers physiological variations in thyroid function due to an interaction several hormones, mainly between HCG and TSH. Since HCG is structurally analogous to TSH, receptor and stimulate the thyroid cells. As a result, significant increase in HCG during the first trimester causes an increase in free T4, with decreased TSH levels. In most cases, decrease in TSH is temporary and need no treatment. However, prolonged increase in FT4 above normal is sometimes associated with transient thyrotoxicosis.
Maternal hypothyroidism is been directly linked with low birth weight infants [Endocrinol Metab Clin North Am 1995; 24(1):41-71]. In another study published in NEJM in the year 1999, researchers have documented an association between undetected sub clinical hypothyroidism during pregnancy and lower IQ in offspring. They have found that 19% of children born to mothers with undiagnosed hypothyroidism during pregnancy had IQ scores of 85 or lower. On the other hand, only 5% of children born to mothers without hypothyroidism have produced IQ level. An IQ below 85 can mean significant impairment for children. These children are more likely to have difficulties in school, and may be less successful in their careers and interpersonal relationships. Researchers predicted that women with untreated thyroid deficiency during pregnancy are 4 times more likely to have children with lower IQ scores.
Another study, which involved 9403 women, was published in the journal of Medical Screening in the year 2000. the rate of miscarriage was significantly higher in pregnant women who have TSH level 6mU/L or more (3.8%), than in women with TSH level less than 6mU/L (0.9%). Furthermore, it was found that, as TSH levels increase, the rate of miscarriage increased incrementally. In women, who have TSH level 10mU/L or more rate of miscarriage was 8.1%. These results suggested that pregnant women with an underactive thyroid have a 4 times greater risk of miscarriage than euthyroid pregnant women during the second trimester (3.8% risk vs. 0.9% risk). Researchers found that 6 out of every 100 late miscarriages can be attributed to thyroid deficiency.
In 2002-2003, a study was done by IPGMER, Kolkata to understand the incidence and the effects of hypothyroidism in pregnancy in Indian population (Jobset Gynecol India 2007; 57 (4): 331 334). The study included 41 pregnant women with hypothyroidism as against 141 age-matched euthyroid pregnant women as controls. The most common maternal complications in hypothyroid women were preeclampsia (21.95% in hypothyroid women vs. 14.89% in euthyriod women), followed by pre-term labour (19.51%). Other complications in hypothyroid women were treated abortions (14.63%), postpartum hemorrhage (4.88%), wound infections (4.88%) and antepartum hemorrhage (2.44%). The most common fetal abnormality was low birth weight (27.03%), followed by neonatal hyperbilirubinemia (13.5%) and higher incidence of neonatal hypothyroidism (10.81%). The authors suggested that endemic iodine deficiency produces combined maternal and fetal hypothyroidism, which increases risk of severe fetal hypothyroidism. They have also found that perinatal mortality rate was high in hypothyroid women (81 per 1000 live births). This could be due to late diagnosis of hypothyroidism in mother due to late presentation, as it is already reported that treated maternal hypothyroidism prevent adverse perinatal outcome (J. Reprod. Med 2006; 51: 59-63). In maternal hypothyroidism, there are placental hypoxic changes, which may cause fetal distress. In this study, of the 41 hypothyroid pregnant women, 21.95% showed other associated medical disorders during pregnancy. These include diabetes mellitus (7.31%), jaundice (4.88%), heart disease (4.88%), hypertension (2.44%) and SLE (2.44%). On the other hand, euthyroid women exhibited only heart disease (4.25%) and hypertension (3.54%) during pregnancy. It should be noted that hypothyroidism is already shown to be associated with other autoimmune diseases like pernicious anemia, vitiligo and type 1 diabetes mellitus (In: Medical Disorders in Pregnancy. Chamberlain G, Steer PJ (Eds.), 3rd edition, London, Churchill Livingstone 2001: 275-297).
In astudy done by osmania university hyderabad .it was demonstrated that 4.29% of women with recurrent pregnancy loos, hypothyroidism was the causative factor for abortion
Referance , health screen, march2009