Relations between Placental Concentrations of Chorionic Somatomammotropin (Placental Lactogen) and Growth: A Study Using the Twin Method

Abstract

ExtractConcentrations of chorionic somatomammotropin (HCS) in extracts of homogenized placentas from 125 viable twin pairs were determined by radioimmunoassay. The intraclass (within-pair) correlation for placental concentration of HCS (C-HCS) was 0.64, and for total placental content of HCS (TPHCS) 0.59, both significant at P < 0.0,01. Individual differences within twin pairs were shown to be related to both fetal and postnatal growth. The co-twin method was used to assess these relations of HCS with growth variables. Twins with relatively lower C-HCS (index cases) were compared with their co-twins with relatively higher C-HCS (control subjects) and differences on growth variables were tested by t test for matched pairs. Index cases had significantly lower placenta weight (P < 0.001), birth weight (P < 0.001), and birth length (P < 0.01). In a similar analysis, index and control cases were separated on the basis of TPHCS, a function of both C-HCS and placental weight. Again, index cases had a significantly lower birth weight, but the relation to birth length was only marginally significant (P < 0.10).Somatic measurements at age 24 months were available for 27 of the pairs who had been followed longitudinally in the Louisville Twin Study. The index cases who had had lower placental C-HCS weighed less (P < 0.02) and were shorter (P < 0.02) than their co-twin control subjects at the age of 24 months. When relative placenta weights or birth weights rather than C-HCS were used to designate index and control cases, there were no clearly significant relations with 24-month measurements; when TPHCS was used, only the relation with weight was significant (P < 0.05). Speculation

Chorionic somatomammotrophin as index of fetal growth.

“…The latter authors do not think that hCS represents a true fetal equivalent of pituitary growth hormone, which is unessential for fetal growth (Blizzard and Alberts, 1956;Reid, 1960;Steiner and Boggs, 1965), but that it produces alterations in maternal metabolism which promote fetal growth indirectly. Our own studies in twins (MacMillan et al, 1973), which showed a strong positive relation between relative twin size and placental hCS concentration, raised the question whether hCS affects fetal growth other than via the maternal circulation.…”