Research Article: Prediction of small-for-gestational age by fetal growth rate according to gestational age

Date Published: April 26, 2019

Publisher: Public Library of Science

Author(s): Min-A Kim, Gwan Hee Han, Young-Han Kim, Andrew Sharp.


Small-for-gestational age (SGA) infants should be identified before birth because of an increased risk of adverse perinatal outcomes. The objective of this study was to assess the impact of fetal growth rate by gestational age on the prediction of SGA and to identify the optimal time to initiate intensive fetal monitoring to detect SGA in low-risk women. We also sought to determine which the ultrasonographic parameters that contribute substantially to the birthweight determination.

This was a retrospective study of 442 healthy pregnant women with singleton pregnancies. There were 328 adequate-for-gestational age (AGA) neonates and 114 SGA infants delivered between 37+0 and 41+6 weeks of gestation. We compared the biparietal diameters (BPD), head circumferences (HC), abdominal circumferences (AC), femur lengths (FL), and estimated fetal weights (EFW) obtained on each ultrasound to determine which of these parameters was the best indicator of SGA. We created receiver operating characteristic curves, calculated the areas under the curves (AUCs), and analyzed the data using multivariable logistic regressions to assess the ultrasound screening performances and identify the best predictive factor.

Among the four ultrasonographic parameters, the AC measurement between 24+0~28+6 weeks achieved a sensitivity of 79.5% and a specificity of 71.7%, with an AUC of 0.806 in the prediction of SGA. AC showed consistently higher AUCs above 0.8 with 64~80% sensitivities as gestational age progressed. EFW measurements from 33+0~35+6 gestational weeks achieved a sensitivity of 60.6% and a specificity of 87.6%, with an AUC of 0.826. In a conditional growth model developed from the linear mixed regression, the value differences between AC and EFW in the SGA and AGA groups became even more pronounced after 33+0~35+6 weeks.

Healthy low-risk women with a low fetal AC after 24 weeks’ gestation need to be monitored carefully for fetal growth to identify SGA infants with a risk for adverse perinatal outcomes.

Partial Text

Small-for-gestational age (SGA) infants are at increased risk of adverse perinatal outcomes such as low Apgar scores, neonatal intensive care unit (NICU) admissions, neurological injuries, stillbirths, and neonatal deaths. Therefore, it is imperative to identify SGA fetuses prior to delivery. Assessing fetal size via ultrasound is the most commonly used and best method available in clinical obstetric practice. Ultrasonography also plays an important role in planning and guiding obstetric interventions for fetuses that exhibit abnormal growth rates [1]. SGA infants identified during the antenatal period that receive appropriate and timely interventions have a four-fold decrease in composite severe morbidity and mortality [2]. Therefore, detecting abnormal growth patterns that can lead to fetal growth restriction and SGA is extremely important during the prenatal period.

This was a retrospective study in which data were collected from the medical records of 442 healthy pregnant women with singleton pregnancies who delivered livebirths between 37+0 and 41+6 weeks of gestation at the Gangnam Severance Hospital between January 2015 and March 2017. Each patient had routine mid-second and third trimester ultrasound examinations for fetal biometry, which is common practice. The 442 women in the study delivered 328 adequate-for-gestational age (AGA) neonates and 114 SGA neonates. The study was approved by the Institute of Review Boards (IRBs) of Gangnam Severance Hospital.

The study population consisted of 442 pregnant women with singleton gestations, who underwent serial ultrasonographic examinations from the 24th gestational week until the time of their full-term deliveries in Gangnam Severance Hospital. We included 114 women who delivered SGA neonates (SGA group) and 328 who delivered AGA neonates (AGA group) after 37 weeks of gestation. The demographic characteristics of the study population are shown in Table 1. There were significantly lower BMIs before pregnancy and at delivery in the SGA group than those in the AGA group. Also, the SGA group had little overall maternal weight gain during pregnancy compared to the AGA group, and the difference was significant. There was a significant difference in birth weight (3309.9 g) in the AGA group compared to the SGA group (2260.1 g) (p<0.001). However, there was no significant difference in the gestational ages at delivery between the two groups. We evaluated the true efficacy of ultrasonography in the prediction of SGA. We investigated the optimal timing for the mid-second and third trimester ultrasounds and the primary biometric parameters facilitating the diagnosis and monitoring of SGA. The findings in this study demonstrated that intensive fetal growth rate assessments and monitoring to predict SGA infants are best conducted via ultrasound measurements of AC at 24+0 ~ 28+6 weeks of gestation. Unrecognized SGA fetuses had a four-fold higher risk of adverse outcome compared with those that were recognized antenatally [9]. Therefore, the antepartum recognition of SGA can improve fetal outcome. The period in which EFW is most predictive in the assessment and monitoring for SGA is 33+0 ~ 35+6 weeks of gestation. AC at 24+0 ~ 28+6 weeks of gestation had a higher sensitivity (80%) for the detection of SGA neonates than EFW at 33+0 ~ 35+6 weeks of gestation (61%), but the specificity was higher for EFW (88%) than AC (72%). Moreover, the AC measurement had higher AUCs (0.8) with 64~80% sensitivities as the gestation progressed. We also confirmed that the AC measurement was more closely correlated to birthweight and the detection of SGA than any of the other ultrasonographic parameters. All ultrasonographic parameters decreased after 24 weeks of gestation and the gap between SGA and AGA group was wider at 33+0 ~ 35+6 weeks’ gestation. On the basis of these results, if the fetal AC at 24+0~28+6weeks’ gestation is decreased in low-risk women without preeclampsia or other growth-affecting pregnancy conditions, subsequent intensive ultrasound monitoring could be helpful in the prediction of SGA neonates, thus decreasing the risk of SGA-related poor neonatal outcomes.   Source:


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