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Table of Contents
ORIGINAL ARTICLE
Year : 2015  |  Volume : 9  |  Issue : 2  |  Page : 51-55

Prevalence of gestational thyroid disorders in Zaria, north-western Nigeria


1 Department of Chemical Pathology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
2 Department of Chemical Pathology, University College Hospital, Ibadan, Nigeria
3 Department of Obstetrics and Gynaecology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
4 Department of Chemical Pathology, Federal Teaching Hospital, Gombe, Gombe State, Nigeria

Date of Web Publication2-Mar-2016

Correspondence Address:
Jibril Mohammed El-Bashir
Department of Chemical Pathology, Ahmadu Bello University Teaching Hospital, Zaria
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0331-3131.177949

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   Abstract 

Background: Thyroid disorders are the second most common endocrine disorders found during pregnancy. Normal maternal thyroid function is critical for normal fetal development. Gestational thyroid dysfunctions complicate pregnancy with a significant increase in maternal and perinatal morbidity and mortality.
Objective: To assess the prevalence of thyroid disorders among pregnant women in Zaria.
Materials and Methods: Study population consisted of 300 apparently healthy pregnant women and 100 apparently healthy age-matched nonpregnant controls. Participants were not on any drug that can affect thyroid function. Serum thyroid hormones [thyroid stimulating hormone, free triiodothyronine (T 3 ), free thyroxine (T 4 ), and thyroid peroxidase (TPO) antibody] were assayed using enzyme-linked immunosorbent assay (ELISA). Data were analyzed using Epi Info 3.5.3 and P-values ≤0.05 were considered statistically significant.
Results: Ages (mean ± SD) were 25.41 ± 5.98 and 26.70 ± 5.83 years for pregnant women and controls, respectively. Parity mean ± SD were 2.32 ± 2.24 and 2.63 ± 2.75 for pregnant women and controls, respectively. The mean gestational age ± SD was 21.68 ± 10.38 weeks. Three percent (3%) were hypothyroid, while 2.3% were hyperthyroid. Nine percent (9%) were TPO antibody positive.
Conclusion: Prevalence of thyroid disorders among pregnant women in Zaria was high therefore routine screening of all pregnant women for thyroid disorders during antenatal care visits may be of benefit.

Keywords: Hyperthyroidism, hypothyroidism, pregnancy, thyroid


How to cite this article:
El-Bashir JM, Abbiyesuku FM, Aliyu IS, Randawa AJ, Adamu R, Adamu S, Akuyam SA, Manu M, Suleiman HM, Yusuf R, Mohammed A. Prevalence of gestational thyroid disorders in Zaria, north-western Nigeria. Ann Nigerian Med 2015;9:51-5

How to cite this URL:
El-Bashir JM, Abbiyesuku FM, Aliyu IS, Randawa AJ, Adamu R, Adamu S, Akuyam SA, Manu M, Suleiman HM, Yusuf R, Mohammed A. Prevalence of gestational thyroid disorders in Zaria, north-western Nigeria. Ann Nigerian Med [serial online] 2015 [cited 2020 Aug 10];9:51-5. Available from: http://www.anmjournal.com/text.asp?2015/9/2/51/177949


   Introduction Top


Thyroid disorders are the second most common endocrine disorders found in pregnancy. [1] These disorders were observed to be four- to fivefolds more frequent in women of child-bearing age when compared with men. [2] Iodine deficiency and autoimmunity are the commonest causes of thyroid disorders worldwide. [1] Disorders of the thyroid gland include overt hypothyroidism, mild/subclinical hypothyroidism, hyperthyroidism, goiter, and thyroid cancers. [1] Pregnancy is seen as a risk factor in the occurrence of thyroid dysfunctions. [3] Recently, more frequent association between pregnancy and thyroid gland pathology has been observed. [3] A considerable number of pregnant women were undiagnosed or insufficiently treated for thyroid dysfunction during pregnancy. [4] Even subclinical hypothyroidism in the presence or absence of thyroid antibodies is regarded as a threat to a woman's fertility, pregnancy outcome, and the development of a child. [4] Various studies on pregnant women in Europe and United States reported prevalence rates of 0.1-0.4% for hyperthyroidism, [1],[5] 0.3-0.5% for overt hypothyroidism, while subclinical hypothyroidism occurs in 2-3%. [1],[5] The prevalence of hypothyroidism and hyperthyroidism among pregnant women in Tunisia were 3.2% and 1.3%, respectively. [6] Goitre belt in Nigeria was described since 1954, some villages along the belt had goitre rates as high as 60%. [7]

Complications in the pregnancies associated with thyroid diseases are complex and serious, with a significant increase in maternal morbidity and perinatal morbidity and mortality. [8] Uncontrolled thyroid dysfunction in pregnancy is associated with adverse fetal and maternal outcomes. Subclinical hypothyroidism has been associated with increased incidence of preeclampsia and postpartum hemorrhage (PPH). [9] Overt hypothyroidism was associated with maternal anemia, [10] PPH, [9] and abruptio placentae. [10]

Fetal outcome in overt maternal hypothyroidism include fetal distress, [11] low birth weight/prematurity, [9],[10] small for dates, [12] breech presentations, [13] congenital malformations, [9] fetal deaths [9],[10],[14] and perinatal deaths, [14] fetal brain damage, and neurodevelopmental anomalies characterized by low intelligence quotient. [15],[16]

Hyperthyroidism in pregnancy is associated with an increase in the incidence of preterm delivery, [17] low birth weight, [18] preeclampsia, [18] maternal congestive cardiac failure, [17] and thyroid storm. [19]

There are common symptoms seen in normal pregnancy and hyperthyroidism such as anxiety, palpitations, dyspnea, weakness, and cardiac systolic murmurs. Symptoms of mild hypothyroidism such as lethargy, weight gain, and constipation are also seen in normal pregnancy. This makes the diagnosis difficult; therefore, a high index of suspicion is required to differentiate between the two.

There is paucity of data concerning thyroid disorders among pregnant women in Nigeria.


   Materials and Methods Top


Four hundred apparently healthy women were recruited for the study. The study sample consisted of 300 pregnant women and 100 age-matched nonpregnant controls. The ages ranged 14-40 years. These subjects were drawn from various antenatal care centers in Zaria, a city in Kaduna state, north-western Nigeria. Controls were recruited from the township community. Only pregnant women who were sure of their last menstrual period that was confirmed from their booking of ultrasound scan and were not on iodine supplement, amiodarone, or any drug that affects thyroid function were recruited for the study after written consent was obtained. Approval to carry out this study was obtained from the Ethical and Scientific Committee of Ahmadu Bello University Teaching Hospital Zaria.

Sample size was determined using the formula n = Z2PQ/d[2],[20] where n represents desired sample size, Z is standard normal deviation set at 1.96 corresponding to 95% confidence interval, P = (27%) [21] is the prevalence of target population with a particular characteristics and Q = 1-P.

Ultrasensitive enzyme-linked immunosorbent assay (ELISA) kits for thyroid stimulating hormone (TSH), free thyroxine (T 4 ), free triiodothyronine (T 3 ), and antithyroid peroxidase (anti-TPO) antibody were obtained from Diagnostic Automation Inc. USA.

Data were analyzed using Epi Info 3.5.3 (Centers for Disease Control and Prevention, Atlanta, GA). The results of thyroid function tests from pregnant women were compared to nonpregnant controls using two-tailed Student's t-test for matched samples. Relative risks and odd ratios were also calculated. TSH concentration above the upper reference value with normal free T 4 concentration was considered subclinical hypothyroidism. High TSH concentration and low free T 4 concentration was considered overt hypothyroidism while low TSH and high free T 4 was considered as hyperthyroidism. Subclinical hyperthyroidism was defined with low TSH and normal free T 4 . P-values ≤0.05 were considered statistically significant.

Trimester specific reference values for our environment were used [22] [Table 1] in keeping with the American Thyroid Association (ATA) recommendation. [23]
Table 1: Demographic profile of the participants

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   Results Top


Demographic characteristics of the participants are shown in [Table 1]. Majority were Muslims, married, and Hausa/Fulani. Level of education varies among the participants. Graduates were the majority among the nonpregnant controls and minority among the pregnant subjects. Forty-two per cent (42%) of the controls and 81% from the pregnant subjects were from monogamous family.

[Table 2] shows the clinical and biochemical characteristics of the study population. Three hundred (300) pregnant women and 100 nonpregnant controls with equally matched ages (mean ± SD) 25.41 ± 5.98 and 26.70 ± 5.83 years (P > 0.05), respectively, were recruited for the study. Seventy-five pregnant (75) women were in their first trimester, 125 in were the second trimester, and 100 were in the third trimester. Parity distribution (mean ± SD) was 2.32 ± 2.24 and 2.63 ± 2.75 among the pregnant women and nonpregnant controls, respectively, of which the differences were not statistically significant. The mean blood pressures (BP) (both systolic and diastolic) were within the normal limits. The systolic BP was 112.7 ± 13.2 and 120.3 ± 20.8 mmHg among pregnant and nonpregnant controls, respectively, while the diastolic BP was 74.9 ± 11.9 and 79.4 ± 14.1 mmHg for pregnant and nonpregnant controls, respectively. Even though the difference of both systolic and diastolic BPs among the controls and pregnant women was statistically significant, they were within normal values. There was no significant difference in the means of thyroid function tests (TSH, free T 3 , and T 4 ).
Table 2: Comparison of clinical and laboratory characteristics of control subjects and pregnant subjects

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[Table 3] shows trimester specific reference values used in the study as recommended by the ATA.
Table 3: Median values and reference intervals for thyroid function test in subjects and controls [50th (2.5th and 97.5th percentiles)]

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Prevalence of thyroid disorders among controls and pregnant women were 5% and 5.3%, respectively. Among the controls, 3% were hypothyroid (1% overt) and 2% hyperthyroid (all subclinical). Three percent (3%) of the pregnant women were hypothyroid (2.7% subclinical and 0.3% overt), while 2.3% were hyperthyroid (all subclinical). Nine percent (9%) of the pregnant women enrolled were TPO antibody positive, while 16% were TPO positive among controls [Table 4]. Odds ratio and relative risk of hypothyroidism in TPO positive mothers are 5.56 and 5.06, respectively (P < 0.05). Odds ratio and relative risk of hyperthyroidism in TPO positive pregnant women were 1.71 and 1.69, respectively (P > 0.05).
Table 4: Prevalence of maternal thyroid disease and antithyroid peroxidase (anti-TPO) antibody status among the subjects and controls

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   Discussion Top


Prevalence of hypothyroidism among pregnant women in Nigeria was found to be 3.0%, subclinical hypothyroidism occurred in 2.7% and overt hypothyroidism in 0.3%. This was higher than the 1.86% reported in an iodine sufficient environment, Moscow in 2003. [24] This may be due to the fact that the TSH upper reference value used in that study was 4.0 μIU/L irrespective of trimester.

According to many population studies, the prevalence of hypothyroidism (both subclinical and overt) in randomized samples of pregnant women was up to 2.5%. [16],[24] This is in agreement with what was obtained in the present study and in Tunisia. [6] In general, overt hypothyroidism was said to occur in 0.3-0.5%, while subclinical hypothyroidism was said to occur in 2-3% of all pregnancies worldwide. [1] This was in strong agreement with the present study.

Prevalence of subclinical hyperthyroidism among pregnant women in this study was 2.3%, none had overt hyperthyroidism. This finding was consistent with a similar study in Moscow where no case of overt hyperthyroidism was reported. [24] This was higher than the estimated worldwide prevalence of 0.1-0.4%. [1] Like the effect of β-human chorionic gonadotropin (hCG), thyrotropin could have possibly played a role in overestimating the prevalence.

anti-TPO antibodies were observed in 9.0% of the pregnant population in this study. Prevalence of autoimmune antibodies was reported to be low among black population. [6],[25],[26],[27] This is lower than 11.8% among first trimester pregnant women in Prague, [28] lower than 27% as reported in Lagos, Nigeria [21] but agrees with 6-19% as reported in Russian pregnant women. [24] Prevalence of TPO is even higher among the controls and its presence in pregnancy increase the risk of gestational hypothyroidism. This is consistent with the finding of Dotun et al. (2009)


   Conclusion Top


In conclusion, prevalence of thyroid disorders among Nigerian pregnant women was high and comparable to that of nonpregnant population. Presence of TPO was a risk factor in developing hypothyroidism in pregnancy. We therefore recommend screening of all pregnant women with at least TSH and TPO at booking to determine the cases of thyroid dysfunction for subsequent management. Establishing of trimester specific reference interval for thyroid function tests is also recommended in keeping with the ATA.

 
   References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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