Fetal bone strength and umbilical cord length.

OBJECTIVE

Activity has been demonstrated in promoting bone mass in infants and adults. One of the major signs of fetal activity may be the length of the umbilical cord. We hypothesized that the fetus with a shortened umbilical cord may have low bone mineralization because of decreased movement or activity.

STUDY

DESIGN

We investigated eight healthy term infants with shortened umbilical cords and 15 control term infants. Mothers with pre-eclampsia or hypertension, chorioamnionitis or prolonged ruptured of membranes were excluded from the study. Mother's age, parity, infants' gender, and birth and placenta weights were recorded. The umbilical cord length and diameter were measured as well as the newborn's tibial speed of sound (SOS). SOS measurements (Sunlight Omnisense 7000P instrument) were obtained at the tibial midshaft.

RESULTS

Measurement reproducibility was 0.8+/-0.6% (mean+/-s.d.) for repeat SOS measures. There were no differences between the two groups in mother's age (24.6+/-5.8 vs 25.8+/-3.3 years), parity (2+/-1 vs 2+/-1), infant's gender (25% females vs 47% females), birth weights (3320+/-451 vs 3409+/-452 g), or placental weights (521+/-69 vs 588+/-105 g). Umbilical cord diameters were also similar, 1.1+/-0.3 vs 1.1+/-0.2 cm. However, there was a difference in the cord length between the two groups, 46+/-2 vs 57+/-4 cm (Mann-Whitney, P<0.001). The newborn infants with the shorter umbilical cord also had lower tibial SOS compared with controls, 3047+/-107 vs 3194+/-311 m/sec (Mann-Whitney, P<0.05). Tibial SOS was related to the infant's umbilical cord length (r=0.57, P<0.01) but not to infant's birth weight, gender, umbilical cord diameter, maternal age, or placenta weight.

CONCLUSION

Infants with a short umbilical cord length have lower bone strength.