Objective: To determine if the growth status at birth of twins can be predicted in the third trimester using the Prenatal Growth Assessment Score (PGAS).
Methods: The growth of 40 twin fetuses were studied with ultrasound from 14 weeks until delivery. Measurements of the head circumference (HC), abdominal circumference (AC), thigh circumference (ThC), femur diaphysis length (FDL), head cube (A), and abdominal cube (B) were made at 2 to 3 week intervals. Rossavik growth models for these parameters were determined from second trimester measurements. These models were used to define expected third trimester growth curves and birth characteristics. Comparisons of expected and actual third trimester measurements were used to calculate PGAS values after various time points (PGASAt) and after the last time point (PGASAT). Similar comparisons after birth were used to determine Growth Potential Realization Index (GPRI) values for HC, AC, ThC, weight (WT), and crown-heel length (CHL), with and without correction for decreased soft tissue deposition. These two sets of GPRI values were used to calculate two sets of Neonatal Growth Assessment Scores (NGASS, NGASTw). Using NGASS and NGASTw (as well as GPRI values in some cases), the twin neonates were classified as Normal (N), Decreased Soft Tissue Deposition, (DSTD), Intrauterine Growth Retardation (IUGR) and Macrosomia (M).
Results: At birth 22/40 (55%) were classified as N, 9/40 (22.5%) as DSTD, 6/40 (15.0%) as IUGR, and 3/40 (7.5%) as M. All -PGASAT values in the N group were greater than -0.40% with one exception (-PGASAT = -0.43%). All PGASAt values were above this same boundary except for one fetus. No differences were seen between the N and DSTD groups [mean -PGASAT (range): N, -0.12% (0% to -0.34%); DSTD, -0.10% (0% to -0.30%)]. The IUGR group had 4 fetuses with -PGASAT values between -0.65% and 2.79% and two with values of 0.0% and -0.12%. Growth retardation in the latter two was limited to a decrease in thigh soft tissue deposition. -PGASAt values in the first 4 fetuses were below -0.40% 1.6 to 9.5 weeks before delivery (mean: 6.1 weeks). Fetuses in group M had +PGASAT values of 0.0%, +1.8%, and +1.2%. PGASAt values were above +0.40% at 3.6 and 9.8 weeks before delivery in the latter two fetuses.
Conclusions: These results support the concept that PGASAT and PGASAt values outside +/- 0.40% indicate either IUGR or macrosomia. Almost all fetuses with growth problems in the third trimester can be detected, on average, 6 weeks before delivery unless the growth abnormality is limited to decreased soft tissue deposition.