Keywords
fetal abnormality - fetal growth restriction - preeclampsia - second-trimester ultrasound
- ultrasound
Introduction
Antenatal assessments of pregnant women in the second trimester in India focus almost
exclusively on the identification of structural and congenital abnormalities through
a targeted imaging for fetal anomalies (TIFFA) at 20 to 24 gestation weeks. A systematic
review from India reported a pooled prevalence of congenital anomaly of 184.48 per
10,000 births (95% CI 164.74–204.21) and 472,177 (95% CI: 421,652 to 522,676) congenital
anomaly affected births in India each year.[1] Congenital heart defects (65.86 per 10,000 live births) and neural tube defects
(27.44 per 10,000 live births) were the most common congenital abnormalities reported.[2] The congenital anomaly termination of pregnancy rate was 4.39 per 1,000 births in
India.[2] Pre-eclampsia (PE) and fetal growth restriction (FGR) cause adverse consequences
that can be minimized by early identification of pregnant women at high-risk.[3]
[4]
[5]
[6]
[7] However, the assessment of PE and FGR is a lower priority than congenital abnormalities
in the second trimester study at 20 to 24 gestation weeks. We estimated the comparative
prevalence of congenital abnormalities, PE and FGR among pregnant women screened between
20 and 24 gestation weeks in the Samrakshan program[8] of the Indian Radiological and Imaging Association (IRIA) to determine if the data
support the larger focus on congenital abnormality.
Method
A standardized trimester specific protocol was used to screen pregnant women between
11 and 14 weeks, 20 and 24 weeks and 28 gestation weeks onward in Samrakshan.[8] Briefly, the assessments included clinical and demographic details, fetal biometry,
estimated fetal weight (EFW), fetal abdominal circumference (FAC), mean arterial blood
pressure, and fetal Doppler studies. An individualized risk for PE was determined
using the online Fetal Medicine Foundation calculator and a cutoff of 1 in 150 was
used to stratify risk.[8] The diagnosis of PE was based on documented evidence in the medical records for
a clinical diagnosis and management of PE after 20 gestation weeks. EFW and/or FAC
<10th percentile were considered as high risk for FGR or suggestive of the presence
of early FGR or small for gestational age (SGA) fetus. Congenital abnormalities were
determined based on a TIFFA scan and fetuses that required further study and fetal
interventions were referred to tertiary care units for further assessment.
Results
We analyzed the data of 4,572 pregnant women screened between 20–24 gestational weeks.
The prevalence of congenital abnormalities (3.81%) was significantly lower (p < 0.001) than women diagnosed with early PE (2.71%) or with a high risk for PE (4.00%)
and women (6.80%) with early FGR or at higher risk for fetal growth restriction with
both EFW and FAC < 10th percentile ([Table 1]). Of the 4,572 women screened at 20 to 24 weeks, 721 (15.77%) had been started on
low-dose aspirin based on the risk assessment at 11 to 14 gestation weeks. Third trimester
assessments until 37 gestation weeks were available for 4,372 pregnant women. At the
third trimester assessment, preterm PE had developed in 1.94% (95% confidence interval
[CI]: 1.55%, 2.43%) of the women considered low risk in the first trimester assessment,
and in 25.40% (95% CI: 21.98%, 29.15%) of women started on low-dose aspirin based
on the first-trimester assessment. Preterm PE did not develop until 37 gestation weeks
in 74.60% (95% CI: 70.85%, 78.02%) of pregnant women started on low-dose aspirin in
the first trimester, which is consistent with the results of a recent systematic review
and meta-analysis that reported a 62% reduction in the in risk of preterm preeclampsia
with low-dose aspirin.[9] The ASPRE trial had also reported a reduction in the risk (OR 0.38, 95% CI: 0.20,
0.74) for preterm PE in women receiving low-dose aspirin compared to placebo.[10] Overall, 4.96% (95% CI: 4.46%, 5.65%) of pregnant women developed preterm PE before
37 gestation weeks. The comparative prevalence at 20 to 24 gestation weeks reaffirms
that the identification of pregnant women with-or-at-risk for PE and FGR in the second
trimester is a priority in this population.
Table 1
Prevalence of congenital abnormalities, preeclampsia, high risk for fetal growth restriction
in the screened population at 20–24 gestation weeks
|
Prevalence
|
95% CI
|
|
Congenital abnormality
|
174, 3.81%
|
3.28, 4.39
|
|
Diagnosed preeclampsia
|
124, 2.71%
|
2.28, 3.22
|
|
High risk for preeclampsia[a]
|
178, 4.00%
|
3.46, 4.62
|
|
Fetal abdominal circumference (FAC) <10th centile
|
378, 8.27%
|
7.50, 9.10
|
|
Estimated fetal weight (EFW) <10th centile
|
395, 8.64%
|
7.86, 9.49
|
|
Both EFW and FAC < 10th centile
|
311, 6.80%
|
6.11, 7.57
|
a Excludes already diagnosed preeclampsia.
Discussion
The identification of a congenital abnormality involves either continuation or termination
of pregnancy, or fetal interventions based on the severity and lethality of the abnormality.
Pregnant women identified as high-risk for PE and FGR are advised low-dose aspirin
starting from 11 to 14 weeks as a preventative measure. Treatment-naïve cases identified
in the second trimester can be started on low-dose aspirin within 20 gestation weeks
but with lower effectiveness. Longitudinal assessments of fetal growth velocity and
interval assessments of FAC and EFW are useful to monitor growth. However, it is a
pragmatic reality that patients do not necessarily follow up with the same doctor
for care and do not have access to or carry their medical records with them for follow-up
assessments. The use of fetal Doppler studies can help identify women at-risk for
PE and FGR. The assessment of Doppler studies is not time consuming and can be integrated
with routine antenatal ultrasound and TIFFA studies.
Clinical algorithms that can identify pregnant women at high risk for PE and FGR between
20 and 24 gestation weeks are available and can be used by fetal radiologists. Fetal
radiologists in India must focus on the development of region-specific and representative
normative biometry and Doppler parameters as a priority and integrate these with the
sonography machines for more accurate risk estimates. The distinction between early
FGR and SGA needs accurate normative data that allow optimal identification and monitoring
of progress. The data on prevalence from Samrakshan show that a larger focus only
on congenital abnormalities in the second trimester is a misplaced priority based
on the magnitude of PE and FGR in the pregnant women population of India.
