JRMS August 2008; 15(2): 34-37 IntroductionThyroid stimulating hormone (TSH), or thyrotropin, is a glycoprotein synthesized and secreted by the thyrotropes of the anterior pituitary gland. It has a molecular weight of about 28,000. TSH stimulates synthesis and secretion of the thyroid hormones, thyroxin (T4) and triiodothyronine (T3).(1) Cord blood is a source for the determination of thyroid related hormones in neonates.
(2) The exposure of the neonate to the surrounding atmosphere after delivery may evoke the anterior pituitary gland to secrete extra hormones of TSH peaking at 30 minutes after birth resulting in an augmentation of conversion of T4-to-T3 in the liver.(3)
Thyroid hormones play an important role in the fetus, since they are essential for the maturation, differentiation and development of many organs, in particular the brain.(4) The various steps of the hormone action on the fetal brain are not well known.(5)
Although the relationship between cord blood TSH level and intra partum stress is well reported, data regarding the relationship between ante partum conditions and cord TSH level is sparse.
(6) Variable studies showed that thyroid hormones were influenced by instrumental deliveries, fetal distress, and failure to progress, and TSH may reach up to or more than 15 mlU/L, while others found that both elective and emergency Cesarean section were not associated with elevated cord TSH(7). Our study was carried to assess the influence of mode of delivery on fetal TSH, T3 and T4.
MethodsThis was a prospective study carried at Princess Haya Hospital over five months period (November 2004-March 2005). From the 882 term deliveries in our department during the period of study, cord blood samples were taken from 150 selected primi and multi-parous term pregnancies and these were enrolled as: (group I) 50 neonates delivered as normal vaginal delivery (35 primi and 15 multi), (group II ) 50 neonates as elective C/S at completed 37 weeks (17 primi and 33 multi) and (group III) 50 as emergency C/S (7 primi and 43 multi) .
We selected mothers for the three groups to be singleton, within the near age group, gestational age, exclusion criteria included mothers with thyroid disease or any medical disorder, neonates with confirmed congenital hypothyroidism proved later on by investigations and clinical features. Cord blood samples were taken immediately for neonates delivered by normal vaginal delivery and C/S either as elective or emergency C/S.Methods of measurements of TSH, T4 and T3 levels were performed using the IMX assay which is a Micro particle Enzyme Immunoassay (MEIA) for the quantitative determination of thyroid stimulating hormone (TSH) in human serum and plasma, the same methods were used for T4 and T3.
Cord blood of 5 ml was taken immediately after delivery from the cord, which is toward the placenta after clamping it close to the neonatal umbilicus, and sent to the laboratory for processing the results of TSH, T4 and T3. The blood samples were allowed to separate for at least 15 min then centrifuged at 4000 rpm for five minutes. If collected out- with normal laboratory hours the blood was stored at 4ċ (maximum 15 hours) before processing the next day. Coefficients of variation were calculated within the assay of hormones.
ResultsData were collected from 150 infants prospectively selectively and immediately after delivery. as shown in Table I the mean birth weight in normal vaginal delivery, emergency C/S and elective C/S was within average weight, the gestational age and the duration of first stage of labor for ND and emergency C/S were within normal range also.
As shown in Table I the neonatal weights were very near and the P value was < 0.05 which was not statistically significant.
As shown in Table II; The mean level of TSH in the cord blood samples taken from neonates delivered by normal vaginal delivery and emergency C/S was significantly lower than in elective C/S ( p<0.005; 5.9±1.0 m I/ml, 5.8.±1.3 m I/ml and 7.4 ± 1.4m I/ml respectively).
Regarding T4 and T3 they were significantly higher in elective C/S than in normal vaginal delivery and in emergency C/S ( p<0.05; T4 and T3 were 4.1±1.1 n g/dl, 6.9+1.5 pg/d L 2.1±1.3 n g/dl 5.5±15 pg/dl and 5.8±1.3 n g/dl and 5.9±2.5 pg/dl, respectively). Mean umbilical plasma concentrations of TSH and thyroid hormones were significantly higher in the elective cesarean than into other two labor groups (p<0.005 for TSH and P<0.05 for T4 and T3).
As shown in Table III, within assay of hormones the coefficients of variation were calculated of TSH, T4 and T3 as (2-5%, 2-7% and 2-6% respectively). Normal vaginal delivery and emergency C/S compared to elective C/S have shown impact on TSH, T4 and T3.
Table I. Parity, birth weight, gestational age and duration of labor in
different modes of delivery
|
Mode
of delivery
|
Parity
|
Birth Weight (g)
|
GA (weeks)
|
Duration of labor
|
|
Primi
No
|
Multi
No
|
Primi
No
|
Multi
No
|
Primi
No
|
Multi
No
|
Primi
No
|
Multi
No
|
|
ND*
|
35
|
15
|
3.150±250†
|
3.300±350†
|
40±0.2
|
39±0.6
|
10±1.5
|
4. ±1
|
|
Emergency
C/S
|
17
|
33
|
3.190± 240†
|
3.270± 200†
|
39±0.4
|
39±0.2
|
5±0.5
|
4±2.1
|
|
Elective
C/S
|
7
|
43
|
3.300± 150†
|
3.330±60†
|
38±0.2
|
38±0.1
|
_______
|
_______
|
*ND= Normal Delivery † P value < 0.05 (not significant)
Table II. Cord blood levels of TSH, T4 and T3 in different modes of deliveries.
|
Hormone
levels with modes of deliveries
|
TSH
|
T4
|
T3
|
|
ND^
|
5.9±1.0 m I/ml *
|
2.1±1.3 ng/ d l **
|
5.5±1.5 pg /ml **
|
|
Emergency
C/S
|
5.8±1.3 m I /ml *
|
2.1±1.9 ng / dl **
|
5.9±2.5 pg /ml **
|
|
Elective C/S
|
7.4 ±1.4 m I /ml *
|
4.1±1.1 ng / dl **
|
6.9±1.5 pg /ml **
|
^ND= Normal Delivery
Normal ranges of TSH, T4 and T3 in our laboratory are (0.40- 4.00 m I/ml, 0.80 -1.90n g/dl and 1.5 -4.10 p g/ml respectively)
* P <0.005, ** P< 0.05.
Table III. Coefficient of variation within assay of hormones.
|
Hormones
|
TSH
|
T4
|
T3
|
|
Coefficient
of variation
|
2-5%
|
2-7%
|
2-6%
|
DiscussionThe fetal thyroid and pituitary thyroid axis start to function late in the first trimester of pregnancy. The secretory activity of fetal thyroid gland begins to increase by mid-gestation and total T4 levels rise progressively in the fetal blood until term.(8) The threshold for negative feed back from thyroid hormones to the pituitary in the fetus is higher as compared to adult. Serum T4 and TSH levels showed a wide scatter or variability. Fetal serum T4 concentration rise from approximately 25 nmol/L at 12 weeks to 128 nmol/L near term, similarly serum TSH gradually rises from 4-8 m IU/L between 12 weeks and term.
The World Health Organization (WHO) has included neonatal TSH as one of the indicators for assessing iodine deficiency of neonates.(9) So it is vital to determine whether the level of TSH is affected by some perinatal factors, like mode of delivery, as in our study, in order to determine exactly the neonatal thyroid status.
Although the relationship between cord blood TSH level and intrapartum stress is well reported, data regarding the relationship between antepartum conditions and cord TSH level is sparse.(6) Cord blood thyroid-stimulating hormone level is elevated among neonates who undergo more perinatal stress, like progressive normal vaginal delivery and instrumental delivery, others found that both elective and emergency Cesarean section were not associatedwithelevatedcordTSH.(7)
In our study, we obtained the same results as in international studies, where we found that the mean umbilical plasma TSH, T3 and T4 concentrations in the labor group including emergency C/S were lower than the elective cesarean section group. Bird obtained similar results that support our findings. These results suggest that labor reduces plasma thyroid hormone concentrations at birth in association with a rise in cortisol.(10)
Tahirovic HF explained that cord blood thyroxin level is reduced in emergency caesarean section, by the induced transient hypothyroxinemia in neonates with birth asphyxia that lead to emergency cesarean section.(11)
However, Lao TT demonstrated that babies born vaginally had statistically significantly higher umbilical cord plasma TSH but similar T4 concentrations than babies born by caesarean section.(6) Also, in neonates delivered by vacuum extraction TSH level was significantly higher than that following normal vaginal delivery, according to Miyamoto N(12) .
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