DISCUSSION:
The number of infants born small for gestation is higher in low and middle-income countries, with prevalence being highest in South Asia5. Such fetus are at higher risk of neonatal morbidity, stillbirth, and neonatal mortality compared to appropriate for gestational age fetus6. Antenatal identification of SGA fetus with structured surveillance of those identified, lowers the risk of adverse fetal outcomes7.
The outcome of the pregnancies, as measured by birthweight of new-born charted on International Foetal Growth Standards Chart from Intergrowth 21st Project showed that out of 500 pregnancies, 13.2% (66/500) resulted in new-borns with birthweight below 10th centile for the period of gestation.
The conventional method of FH palpation detected SGA foetus in 52/500 women (10.4%), of which, 46/52 pregnancies (69.6%) resulted in new-borns with birthweight below 10th centile (True Positive), and 6/52 (11.5%) were over diagnosed. SGA new-born was correctly ruled out in 95.5% (428/448) pregnancies, while 4.5% (20/448) were missed (Fig.2).
SFH measurement charted on Intergrowth 21st Project charts detected SGA foetus in 57/500 women (11.4%). Among these, 55/57 pregnancies (83.3%) had new-borns with birthweight below 10th centile (True Positive) and 2/57 pregnancies (3.5%) were over-diagnosed (False Positive). The method correctly ruled out small for gestational age neonate in 97.5% (432/443) pregnancies (True Negative) and missed 2.4% (11/443) cases (False Negative) (Fig.2).
A total of 21 cases of SGA new-borns were missed during the study, of which 10 cases were missed solely on conventional FH palpation, 10 cases were missed by both the methods and one by only SFH measurement. Overall, FH palpation missed 20 cases of small for gestational age new-born while SFH measurement missed 11 cases.
Of the 10 cases missed by both methods, all had healthy babies. Seven cases (7/10) had a neonatal birthweight of 2.5 kg or above, which is above the accepted cut off 2.5 kg for Indian standards. Remaining 3/10 cases with a birthweight below 2.5 kg (LBW) were babies born to mothers with a short height (two were 150 cm, and one 149 cm compared to mean height of 154.2 cm in the study population). All these three new-borns were healthy, possibly constitutionally small and were shifted to mothers’ side.
Of the 10 cases missed only on fundal height palpation, 5/10 cases had birthweight ≥2.5kg, which, though below 10th centile for the gestational age on Intergrowth 21st growth chart, is more than the accepted cut off for Indian population. All these babies were born healthy. Remaining 5 cases had birthweight below 2.5 kg, 4 out of 5 were in mothers who had short maternal height (146 cm, 146 cm, 148 cm and 150 cm compared to a mean height of 154.2 cm in study population). All these babies were born with normal APGAR score and shifted to mothers’ side after birth and were possibly constitutionally small. One of the missed cases was a pre-term birth and required neonatal ICU admission.
One case of SGA new-born missed solely on SFH measurement, had a birthweight of 2.5 kg, acceptable as normal in Indian context.
Clinically, FH palpation over-diagnosed SGA foetus in 6 cases, all of which had a birthweight above 2.5 kg. Four cases were over-diagnosed possibly due to engagement of foetal head in the last trimester with resultant decrease in estimated fundal height. One case was over-diagnosed in a woman with a tall height (165 cm) as compared to the average height of study population (154.2 cm). This could be due to increased length of maternal torso, leading to under-estimation of fundal height. One case had a birthweight falling just above 10th centile for the gestational age (2.5 Kg at 37+5 weeks gestation) and could be due to subjective variation in assessment.
SFH measurement missed detection in 11 cases, of which 10 cases were also missed by the method of palpation.
Two cases were over-diagnosed on SFH measurement, one had a birthweight of 2.6 kg, and other case had a birthweight falling exactly on 10th centile, and therefore was not included in small for gestational age as per the cut off value of below 10th centile as per definition.
Symphysis fundal height measurement used as a measure for detection of SGA new-born had a positive predictive value of 96.49% and a negative predictive value of 97.52%, a positive likelihood ratio of 180.3, a negative likelihood ratio of 0.17 and an accuracy of 97.4% (Table 1)
Fundal height palpation for detection of SGA new-born had a positive predictive value of 88.46% and a negative predictive value of 95.54%, a positive likelihood ratio of 50.4 and a negative likelihood ratio of 0.31. The method had an accuracy of 94.8%. The agreement between the two methods for detecting SGA new-born as measured by Cohen’s Kappa Statistic showed a Kappa value = 0.804, indicating a substantial agreement between the two methods for detection of SGA new-born.
In low-income countries, growth restriction has been found to be significantly associated with admission in special baby care unit8. Similar observations were made in the study with a higher proportion (12.1%) of total SGA neonates requiring Neonatal ICU admission compared to 1.2% of AGA neonates (p<0.001). Pre-term delivery was higher among SGA newborn (9.1%) than in AGA newborns (5.3%), and more perinatal complications were seen in SGA newborns (15.2%) compared to AGA newborns (3.7%).
The percentage of fetus born small for gestation (13.2%) was comparable to the prevalence of SGA studied in Indian tertiary care hospital (13.6%)9.
Strengths and Limitations: The strength of the study lies in the application of customised growth charts developed from international standards involving geographically diverse regions including Indian population. The dating of pregnancy was good in the study population.
The main limitation of this study was a lack of ultrasound biometry and doppler correlation to compare the fulfilment of Delphi criteria for foetal growth restriction among those detected to be < 10th centile but >3rdcentile on estimated foetal growth charts by 21stIntergrowth.
Also, the International foetal growth standards estimated foetal weight charts by Intergrowth 21st Project used as an outcome measure, have higher birthweight cut offs for the 10thcentile compared to that for Indian population, which could potentially lead to over-diagnosis of foetal growth restriction.
The measurements and palpation involved in the study are subject to variation according to the built of the mother, and other possible anatomical variations. Also, the frequency of measurement, interval between measurements, and experience of the performer can further affect the study outcome.