The Comparison of Thyroid
Function Tests in Cord Blood Following Cesarean Section or Vaginal
Delivery
Ramezani Tehrani F, Aghaee M, Asefzadeh S.
Qazvin University of Medical Sciences, Qazvin, I.R. Iran.
Correspondence: Fahimeh Ramezani Tehrani, Qazvin
University of Medical Sciences, Qazvin, I.R. Iran.
E-mail:
frtehrani@yahoo.com
Introduction: The present study was designed to assess the influence of mode
of delivery on fetal pituitary-thyroid axis. Materials and Methods: The
endocrine profile (umbilical venous plasma) of three groups of term
infants was compared immediately after delivery. Samples were taken
after 30 vaginal deliveries, 30 emergency cesarean sections during labor
and 30 elective cesarean sections before labor. The study was performed
in the Kowsar Hospital in Qazvin. The samples were matched based on
maternal age, parity and gestational age and none of them had previous
history of medical complications. Measurements of TSH and thyroid
hormone levels were performed using immunoenzymometric and radioimmuno
assays, respectively.
Results: Mean cord plasma TSH level of vaginal and emergency cesarean
section was significantly lower than that of the elective cesarean
section (p<0.0001; 3.3±1.8, 9.0±3.2 and 12.1±6.4 µU/mL, respectively).
Mean concentrations of T4 and T3 were significantly higher in the
elective cesarean section as compared with the emergency cesarean
section and vaginal deliveries (p<0.05; 8.5±1.3, 7.4±2.4 and 7.4±1.3
µg/dL for T4 and 76±12, 62±20 and 51±16 ng/dL for T3, respectively).
Conclusion: These results suggest that labor may reduce plasma
thyrotropin and thyroid hormone concentrations at birth.
Key Words: Labor, Thyroid hormones, Cesarean section,
Hypothyroidism.
Introduction
Neonatal exposure to cold extrauterine environment at the time of
parturition may evoke a marked and transient elevation of TSH peaking at
30 minutes after birth resulting in an augmentation of hepatic T4-to- T3
conversion. The TSH surge stimulates T4 secretion and thyroid conversion
of T4 to T3 and there is a further concomitant increase in hepatic T3
production from T4.1
Some researchers reported that plasma concentration of thyroid
hormones remain lower in cesarean section infants over the first 24
hours of life in comparison to other modes of delivery.2-6 Other studies
indicated that labor pain, duration of labor, and uterotonic agents had
no effect on cord serum TSH and thyroid hormone levels and only the mean
cord serum TSH in vacuum extractions was significantly higher than that
of normal vaginal delivery and cesarean section.7,8 Fuse et al reported
that there was no significant difference among the infants who were
delivered vaginally, by vacuum extraction, or by cesarean section.9 All
the studies emphasized that the difference between cord TSH levels in
various modes of deliveries were transient and the elevation of cord TSH
reflected delivery stress, which would not interfere with the detection
of congenital hypothyroidism in the screening programs using primary TSH
test on the fifth day of life.6 TSH levels of all normal babies
correspond after 2-4 days. Neonatal plasma concen-trations of thyroid
hormones are known to peak within 2 hours of birth,2 but the influence
of labor on both endocrine and metabolic profiles in neonates
immediately after birth remains unclear.
Our study was designed to examine the influence of labor on the fetal
plasma concentration of TSH and thyroid hormones immediately after birth
by comparing umbilical concentrations in groups of babies delivered
after labor (vaginal or cesarean section) with a group delivered before
labor (elective cesarean section).
Materials and Methods
The babies from 90 uncomplicated primparous term pregnancies were
studied. None of the mothers had previous history of thyroid disease,
diabetes, prolonged rupture of membrane, pre-eclampsia and hypertensive
disorder nor were they taking thyroid affecting medications. 30 labors
ended with vaginal delivery and 30 required emergency cesarean section
(labor groups). A further 30 had an elective cesarean section before
labor (non-labor group). The cases were matched with respect to maternal
and gestational age. Umbilical venous blood samples diluted with heparin
were obtained immediately after birth from a double clamped segment of
the umbilical cord. After centrifugation, the plasma was collected and
sent to the referral laboratory.
Umbilical plasma TSH concentration was measured using a two-site
immunoenzymo-metric assay and triidothyronine (T3) and thyroxine (T4)
levels were measured using radioimmuno assay. Limits of detection and
intra- and interassay coefficients of variation for all hormone assays
are given in Table 1.
Mean values were compared using one-way analysis of variance
(ANOVA) and p values less than 0.05 were considered to be significant.
Table 1. Limits of detection, inter and
intra-assay coefficients of variation (CV) for hormone assays
Results
Mean ± SD maternal age was 23.2±4.1 years. Mean gestational age was
similar in labor groups, but it was one week shorter in the elective
cesarean section group (Table 2).
Table 2. Mean birth weight, gestational
age, and duration of labor and neonatal sex
The duration of labor was similar between vaginal and emergency
cesarean section groups. There was no significant difference in birth
weight or sex distribution among the groups (Table 2). 85.1% of mothers
in the emergency- and 90.4% of mothers in the elective cesarean section
groups received halothane general anesthetic and the remainder were
administered local spinal blockage. No one in the vaginal group received
local or general anesthetic.
All babies started breathing rapidly after birth and had normal Apgar
scores of 8-10. Mild respiratory distress (transient tachypnea) was
observed in 4 babies of the elective cesarean section group, but no
medications were needed.
Table 3 demonstrated the mean umbilical plasma concentrations of T3,
T4 and TSH of babies in emergency cesarean section group, according to
the reasons for cesarean section.
Table 3. Mean plasma concentrations of
T3, T4, and TSH by various reasons for the emergency cesarean section
Table 4 shows umbilical plasma concen-trations of TSH and thyroid
hormones of the different groups. Mean umbilical plasma concentrations
of TSH and thyroid hormones were significantly higher in the elective
cesarean than into other two labor groups (p<0.0001 for TSH and P<0.05
for T4 and T3).
Table 4. Mean plasma concentrations of
TSH, T3 and T4 by modes of delivery
Discussion
This study indicates the important influence of the labor process on
the hypothalamic- pituitary-thyroid axis at birth.
In the current study, like Bird’s, the mean umbilical plasma TSH, T3
and T4 concen-trations of the elective cesarean section group were
higher than the labor groups.2
However, some previous studies reported that there was no relation
between cord TSH, T3 and T4 values and the delivery route, duration of
labor or uterotonic agents.7-10 Miyamoto demonstrated that the mean
plasma venous TSH concentration of the babies following elective
cesarean section was lower than that of normal vaginal delivery.6 Also,
the mean serum TSH level in the neonates delivered by vacuum extraction
was higher than the others. He mentioned that delivery stress might
affect the hypothalamic-pituitary-thyroid axis at the birth.6 Gemer also
observed that fetal distress during labor is associated with higher TSH
levels.11
Some differences were noted between the results of the present and of
previous studies that may be due to different time of specimen
collection and also the lack of the studies to stratify the cesarean
section into elective or emergency types of deliveries.
The increase in serum thyrotropin level during the early minutes
after birth is due to exposure of neonates to the cold extrauterine
environment.1,3 Infants delivered by cesarean section have lower
axillary, and skin temperature than those delivered per vaginum.3
Therefore, lower body temperature of the neonate in cesarean section
maybe a stimulus for the higher TSH levels, which evokes increased
secretion of T4 and T3 by the thyroid.
These adaptations may be the stimulus for the subsequent surge of TSH,
which increases the thyroid hormone levels over the first few hours
after birth. Further studies for explaining the exact mechanism of
thyroid hormone changes after labor pain are recommended.
However, mean TSH levels of neonates on days 3-5 in heel blood
spotted filter paper were not significantly different among the three
groups.12,13 It is therefore preferable to obtain blood samples on the
fifth day of life for the congenital hypothyroidism screening TSH
test.14
The mothers’ plasma concentrations of thyroid hormones and
antithyroid antibodies were not checked in the present study and
undiagnosed hypothyroidism of pregnant women may adversely affect the
results. Data from normal pregnant female population demonstrated that
more than 10% have positive levels of thyroid antibodies,14 so it is
recommended to assess the levels of maternal thyroid hormones and
antithyroid antibodies in future studies. Also, it is better to re-check
the plasma concentration of thyroid hormones 2 hours after birth for
evaluation of transient changes of these hormones by different routes of
delivery.
We could not study the effect of fetal distress because of the
limitation of sample size, therefore, further investigation on larger
number of cases is recommended.
Acknowledgement
We thank Dr. Naji for his kind assistance with the measurement of
thyrotropin and thyroid hormone levels in our plasma samples.
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