Chorionic somatomammotrophin as index of fetal growth.
Extract: Concentrations 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 HGS (C-HGS) was 0.64, and for total placental content of HCS (TPHCS) 0.59, both significant at P < 0.001. 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 &;lt; 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: In this study the maternal levels of HCS are common to both members of a twin pair and are not a factor. Placental HCS concentration and total content of HCS were found to be related to birth weight, which suggests that they are valid indices of general placental function. However, the finding that length at birth and at 24 months was best predicted by HCS concentration suggests that HCS production may represent an influence independent of general placental function.