Introduction As the pregnancy advances beyond term, the risk of perinatal morbidity and mortality increases. Hence to prevent these complications associated with postterm pregnancy, induction of labor is done, as per our institution protocol between 40 and 41 weeks of gestation. Induction has its own drawback, so it is essential to identify the women with high chances of failure of induction of labor, to prevent the morbidities associated with induction failure.
Aim To study the role of ultrasonographic fetal adrenal gland enlargement for the prediction of success of labor induction among primigravida beyond 40 weeks gestation.
Material and Methods Low-risk primigravidas beyond 40 weeks gestation, scheduled for induction of labor, were enrolled for the study. Fetal adrenal gland dimensions were measured by using abdominal probe Philips HD 7XE and general electronics logiq P6 pro or any ultrasound machine equipped with 7.5–10 MHz linear array probe and 3.5–5 MHz curved array probe.
Results The fetal adrenal gland length, width and ratio were statistically significant between the successful versus failed induction groups. The cutoff fetal zone ratio > 0.36 for the prediction of successful induction of labor had 90% sensitivity, 89% specificity, 93% PPV and 75% NPV.
Conclusion Fetal zone enlargement (fetal zone ratio > 0.36) is a strong predictor of successful induction of labor as compared to TVL and Bishop’s score. It can be used for screening the women, who are destined for induction failure, so that adverse effects of induction of labor can be avoided.
Keywords : Postterm pregnancy · Fetal adrenal gland · Fetal gland ratio · Fetal zone ratio · Fetal adrenal gland enlargement
Prolonged pregnancy defined as pregnancy at and beyond
41 weeks of gestation is most common challenging condition,
currently faced by obstetricians, because of increased
morbidity and mortality [1, 2].
The risk of perinatal mortality increases twofold at
42 weeks, fourfold by 43 weeks and fivefold to sevenfold
at 44 weeks [3]. The risk of meconium aspiration syndrome
increases by 0.24–1.42%, risk of neonatal acidosis, 5-min
APGAR score less than 7 and admission to NICU increases
progressively [4]. Hence to prevent perinatal morbidities
associated with postterm pregnancy, we often induce
the patient as per our institution protocol between 40 and
41 weeks of gestation.
Postterm pregnancies per se do not put the mother
at risk but the increased morbidity incidental to the hazards
of induction like failed induction, increase in labor dystocia (9–12% vs 2–7% at term) and severe perineal injuries
(3rd–4th degree) related to macrosomia (3.33% vs 2.6%
at term), operative vaginal delivery and a doubling in the
rate of cesarean delivery (14% vs 7% at term) [1].
So, it is essential to identify the women with high chances of failure of induction of labor, to prevent the morbidities associated with induction failure. Hence, there is a need for a marker for the prediction of successful induction. Various screening methods have been studied so far to predict the outcome of induction that includes digital assessment of cervix using Bishop’s score, radiological assessment of cervical length using transvaginal ultrasound and biochemical factors such as fetal fibronectin, interleukin 8 and phIGFBP-1 [5–7].
Measurement of fetal adrenal zone enlargement has emerged as a new modality for the better prediction of success of induction of labor. The adrenal glands are composed of two heterogenous type of tissue, the outer one is cortex derived from intermediate mesoderm and inner one is medulla which is derived from neural crest ectodermal in origin [8–11]. Adrenal cortex tissue first appears at 33 days of fertilization. It differs from its adult counterpart as it is composed of two distinct zones, the inner part is fetal zone and outer part is definite zone (Fig. 1). Inner fetal zone is enzymatically active region and produces large amount of adrenal androgens that are used by placenta for estrogen biosynthesis [11, 12]. On ultrasound, the fetal adrenal gland appears as oval or pyramidal in shape in longitudinal dimension and lentiform or discoid shape in transverse.
It visualized at the end of first trimester but is only reliably visualized by the end of 20 weeks of gestational age. Its size increases linearly from 12 to 17 weeks of gestation. It appears as echogenic central stripe with surrounding hypoechoic rim [13]. During midgestation, the fetal zone occupies most of the cortical volume and produces 100–200 mg/dl of DHEAS, an androgen and precursor of both androgen and estrogen. Fetal zone also produces cortisol that has a role in prenatal development of organs especially maturation of lungs. Cortisol has a role in expression of number of placental genes that result in raised level of corticotrophin-releasing hormone (CRH) and prostaglandins. Prostaglandins have a direct role in parturition, whereas CRH by various mechanisms such as inducing myometrial contractions, dilatation of uterine vessels, stimulation of smooth muscle contraction and increase production of PGF2a and PGE2 leads to successful labor. So, activation of fetal hypothalamus pituitary adrenal axis causes significant enlargement of fetal zone, which indicates fetal readiness for labor and by measuring it we can predict the success of IOL [11, 12].A total of 140 women were enrolled and were categorized
into two groups: Group I (successful induction group) comprised
of 103 women, and group II (failed induction group)
comprised of 37 women.
Mean age was 23.24 ± 3.14 years, and majority 66 (47%)
women were educated till secondary in the study population.
The mean BMI of the study population was 23.22 ± 3.24 kg/
m2.
Among group I, mean of fetal zone length (l), mean of total gland length (L) and the mean ratio of l/L were 1.45 ± 0.24, 2.9 ± 1.2 and 0.50 ± 0.09, respectively, while in group II, mean of fetal zone length (l), mean of total gland length (L) and the mean ratio of l/L were 1.1 ± 0.12, 2.8 ± 0.34 and 0.39 ± 0.08, respectively (p value = 0.01). The comparison was statistically significant between the two groups. This showed that the successful induction had large fetal zone length ratio (Table 1).
The mean of fetal zone width (w), the mean of total gland width and the mean of ratio (w/W) were 0.40 ± 0.03, 0.99 ± 0.45 and 0.415 ± 0.05, respectively, in group I while the mean of fetal zone width (w), the mean of total gland width and the mean of ratio were 0.22 ± 0.02, 0.74 ± 0.24 and 0.29 ± 0.06, respectively, in group II. The fetal adrenal width and ratio were statistically significant between the two groups (Table 1).
The sensitivity and specificity of fetal zone width ratio (w/W) was 84.5% and 89.2%, respectively, which was better than the sensitivity and specificity of fetal zone length ratio (l/L). By using ROC curve comparative analysis, we determined that the fetal zone width ratio (w/W) showed superior predictive value compared with l/L. Accordingly, the fetal zone width ratio (w/W) was used as a measure of fetal zone enlargement (FZE) or FZR (Table 2, Figs. 3 and 4).
For the prediction of successful induction of labor, the cutoff value of Bishop’s score was 4 based on ROC curve having maximum area under curve at Bishop’s score 4, i.e., 0.78. Bishop’s score of group I had mean of 4.49 ± 0.92 while the Bishop’s score of group II had mean of 3.35 ± 1.03. The comparison was statistically significant between the two groups. This showed that the higher Bishop’s score was more favorable for successful induction and suggests
