Nausea and vomiting are common phenomena in pregnancy. In a prospective study done in Hong Kong over a six-month period, it was found that three quarters of pregnant women had either nausea or vomiting during pregnancy.1 The analyzed patient population was comprised of 1,453 women of lower socioeconomic class with a singleton pregnancy. Fifty-one patients were excluded because the severity of nausea and vomiting during early pregnancy was not recorded. No symptoms were reported by 24.8% of the study population, 11.4% had only nausea, 63.5% had both nausea and vomiting, and 0.3% had hyperemesis gravidarum, defined as vomiting so severe as to require hospitalization, but unassociated with underlying diseases, e.g., appendicitis, pyelitis, etc. The age and parity did not differ among the four groups. (This study shows that the incidence of nausea and vomiting of pregnancy [NVP] is similar in both eastern and western populations. The findings disprove any statement that NVP is a phenomenon of western culture and is not present in the oriental population. Rather, this belief is likely due to the paucity of reports in English for other racial groups.)
Antenatal complications were not different between the two groups: anemia, impaired glucose tolerance, gestational diabetes, cardiac and thyroid diseases. We incidentally found that the NVP group had a borderline increased incidence of antenatal haemorrhage (vomiting: 21(), nausea without vomiting: 2, hyperemesis gravidarum: 0, no symptoms: 1(), where represents p < 0.02). Methods of delivery were the same among all groups, as were birth weights of the babies and placental weights. Pregnancy outcomes between vomiting and non-vomiting patients were similar for gestational age, birth weight, parity, congenital anomaly, and perinatal morbidity and mortality.
In another study a final cohort of 74 patients suffering from hyperemesis gravidarum was reviewed.2 Hyperemesis gravidarum was defined according to Fairweather's criteria3, i.e., vomiting occurring in the first 20 weeks of pregnancy of such severity as to require the patient's admission to hospital but which is unassociated with coincidental conditions such as appendicitis, pyelitis, etc. None of the patients smoked. Patients with hyperemesis gravidarum were subdivided into two groups according to the severity of their condition. They were classified as severe (48 cases) if they had one or more of the following: heavy ketonuria (3+ on ketostix), increase in urea and creatinine concentrations, serum electrolyte disturbance, or increase in haematocrit (> 0.43). The other patients were classified as having mild hyperemesis (26 cases), although most had ketonuria (2+ or less on ketostix) and required intravenous therapy. The birth weight and gestation at delivery of the two groups were compared against a group of 8,802 consecutive deliveries at the hospital.
The mothers' mean ages and mean gestation at delivery were not different among the three groups. The mean birth weight of the babies in the severe hyperemetic group was significantly lower than in the mild hyperemetic group (2,950 ± 475 g, 3,159 ± 314 g, p < 0.05) and lower than in the control group (2,950 ± 475 g, 3,221 ± 452 g, p < 0.001). This may imply that the metabolic disturbance created during the period of vomiting may have led to an adverse intrauterine environment which could have affected the growth of the baby.
The incidence of hyperemesis gravidarum was 12.8/1000 in a recent study. This was higher than the rate reported in a similar study population in 1987.4 Most patients were either pregnant for the first time or had previous pregnancies with an unfavourable outcome. About 40% had abnormal thyroid function at the time of admission. There was one molar pregnancy, one partial mole, and two other patients subsequently had their pregnancies terminated. Molar pregnancy is very common among southern Chinese women. We also found that hyperemesis gravidarum is more common among patients with molar pregnancies, but not all patients with molar pregnancies have hyperemesis; therefore, some subunit of human chorionic gonadotropin (hCG) could account for pregnancy vomiting. Among those patients who continued their pregnancies, the incidence of antenatal complications was not significantly different from the general population. The mean birth weights of babies born to hyperemetic patients with abnormal thyroid function, normal thyroid function, and non-hyperemetic patients were 3,075 g, 3,244 g, and 3,184 g respectively. The perinatal outcome was generally satisfactory.
In 23 patients with hyperemesis gravidarum presenting at an average of 10 weeks' gestation, we measured thyroxine (T4) levels.5 Free and total T4 were determined every two weeks until normalization, then at the end of the second trimester and between 35 weeks and delivery. The outcome of the pregnancies, in terms of birth weight and gestation at delivery, was unrelated to the serum thyroxine level, except for a weakly negative correlation between free T4 at second trimester and gestation at delivery ® = -0.434, p < 0.04). Our experience has shown that most patients with transient hyperthyroidism of pregnancy had spontaneous resolution and that treatment of this phenomenon is not required.
Again, no difference was shown in a total of 39 consecutive patients with hyperemesis and either normal or abnormal thyroid function.6 Seventeen patients had hyperthyroxinaemia compared to 22 patients with normal T4 (287.8 ± 161.6 nmol/L, 117.6 ± 20.1 nmol/L, p < 0.001). Their T3 uptake was also higher (31.3 ± 8.1%, 25.9 ± 2.0%, p < 0.05). However, there was no difference between the groups in TSH or thyroid binding globulin (TBG), both being within normal limits. The two groups were similar with regard to maternal age, parity and past obstetrical history. The type of labour and mode of delivery were similar, as were the mean gestation and birth weights of babies. There was no difference in foetal sex ratio or in the incidence of neonatal complications. It should be noted that two patients in the hyperthyroxinaemic group eventually received antithyroid treatment. The first patent had a relapse of hyperemesis and developed clinical hyperthyroidism, and the second patient remained persistently thyrotoxic. Both received courses of methimazole resulting in marked improvement, the first stopping at 28 weeks and the second at term, with no relapses.
Based on our study findings, therefore, women with hyperemesis gravidarum have a similar incidence of pregnancy complications as the general obstetric population and the perinatal outcome is also satisfactory.
In a study on erythrocyte zinc concentration it was found that erythrocyte zinc concentration was inversely related to the serum thyroxine level of the previous three months.7 Erythrocyte zinc reflects the level of carbonic anhydrase enzyme in the red blood cell. In pregnancy, erythrocyte carbonic anhydrase concentration rises with advancing gestation. Thyroid hormones depress the synthesis of carbonic anhydrase and the erythrocyte zinc concentration has been found to be reduced in patients with thyrotoxicosis. The lowest erythrocyte zinc concentration was measured in pregnant patients with underlying thyrotoxicosis, and it was significantly lower than the erythrocyte zinc concentration in normal pregnancies and patients with transient hyperthyroidism associated with hyperemesis gravidarum.
Erythrocyte zinc concentrations may prove useful in determining whether hyperthyroxinaemia in pregnancy is an indicator of clinical thyroid disease.
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