Mechanisms of twinning. I. Effect of environmental diversity on genetic expression in monozygotic multifetal pregnancies.

OBJECTIVE: To examine, using fingerprint homology, the interaction of genetic and environmental factors in arriving at the final phenotypic expression in uniovular triplets, quadruplets and quintuplets. STUDY DESIGN: The fingerprints of several multifetal sets were collected and matched. A total of 250 fingers were printed. A comparison based on the classic dactylographic patterns was made. Zygosity of each set was known from placental chorionicity studies, as well as blood typing and physical similarities. RESULTS: As the monozygotic set size increased, the ipsilateral print concordance diminished. At one extreme, with twins there is 88% homology; at the other end, with quintuplets the correspondence is 71%. CONCLUSION: The overall trend of these results paralleled increasing intrauterine environmental diversity and tended to support the volar pad pressure hypothesis of prenatal fingerprint development.

Mechanisms of twinning. II. Laterality and intercellular bonding in monozygotic twinning.

OBJECTIVE: To utilize observations on laterality and handedness to gain insight into the initiating mechanism of monozygotic human quadruplets. STUDY DESIGN: In a study of thumbprints and handedness in sets of monozygotic quadruplets, homolateral and heterolateral comparisons were used to distinguish mirror-image from symmetric divisions. RESULTS: Data were consistent with a mechanism involving a mirror-image duplication in the first division and a subsequent symmetric separation of the daughters. In addition, these data failed to substantiate a genetic linkage between dermatoglyphics and handedness. CONCLUSION: Reported and reviewed data tend to support the analogy of monozygotic polyembryony in armadillos and humans. The plausible roles of delayed implantation and intercellular bonding are explored, especially as they relate to ambient calcium concentration. Factors tending to enhance the likelihood of monozygotic twinning include calcium channel blockers, lactation, ovulation induction and prolonged in vitro fertilization incubation.

Mechanisms of twinning. IV. Sex preference and lactation.

OBJECTIVE: To examine the likelihood of twinning through conception during lactation and to attempt to explain why there is an increased sex ratio with monozygotic twinning. STUDY DESIGN: Parturients who had become pregnant while still breastfeeding were asked to supply information about their gestations. Also, records from two maternity services over a three-year period were examined for the sex of monozygotic twin sets. Zygosity was confirmed with the pathology reports of the placentas. RESULTS: Much like that in a previously published study, the sex ratio (females/total) was found to be 0.60 in monozygotic twins. In the case of lactating gravidas, the incidence of twinning was much higher than in a random population (11.4% versus 1.1%). CONCLUSION: These findings are consistent with the model of twinning as a consequence of a depressed calcium environment and its effect on embryonic intercellular bonding.

Mechanisms of twinning. III. Placentation, calcium reduction and modified compaction.

OBJECTIVE: To elucidate phenomena contributing to the maintenance and persistence of early uniovular pregnancies. It is proposed that the decreased survival of monozygotic (MZ) multifetal gestations is related to a smaller uteroplacental junctional (UPJ) area during and following implantation when compared with dizygotic (DZ) pregnancies. STUDY DESIGN: Pertinent placental data were collected and analyzed. From this information the placental area was calculated, and an estimate of the size of the UPJ was derived. RESULTS: In the first part of the study, MZ twins, triplets, quadruplets and quintuplets displayed a decrease in mean placental area per neonate as the number of fetuses increased in each set. In the second part, as predicted, MZ twin placentas exhibited smaller placental junctional areas than DZ. This is seen as a direct result of decreased trophectoderm mass due to scission in early gestation. CONCLUSION: These data are consistent with the general impression that multifetal pregnancies, especially monozygotic, are more at risk than singletons because of diminished placental support per fetus. They also reinforce the proposal that the key to MZ twinning is depressed calcium levels.

Rapid spot tests for identifying suspected semen specimens.

The application of a new method for rapidly and conveniently solubilizing, identifying, and semi-quantitatively measuring acid phosphatase and/or zinc in moist and dried materials suspected of containing traces of semen is described. The simplified procedure, intended for field testing outside the laboratory, is performed by rolling a test swab on the moistened specimen and noting characteristic color changes in the swab, which are indicative of the analytes under investigation being above or below certain preselected definitive concentration cutoff levels. The stabilized test swabs consist of bibulous material impregnated with particular amounts of colorimetric reagents. Studies described here report that vaginal washings should be evaluated within 24 h of deposition, that dried specimens can be analyzed many days or weeks after collection, and that results are independent of the sperm count.

Forces affecting the dynamics of labor. A biophysical perspective.

In an effort to comprehend the role of various parameters affecting the rate of obstetric labor, the physical and biochemical factors involved were reviewed. In particular, the forces acting to dilate the cervix were examined mathematically. The increase in the rate of dilation as labor progresses is the direct consequence of the interaction of the applied forces and changes in the chemical characteristics of the cervix. In this way, empirical observations that have been made in the delivery suite can now be understood in terms of the fundamental scientific phenomena active in promoting labor.

Testicular feminization syndrome. An unusual case with high estrogen levels.

In an unusual case of testicular feminization, the patient had a high estrogen and low testosterone level. The source of this female hormone excess may have been functioning gonadal stroma of either female or male derivation. All other aspects of the case were consistent with classic examples of the syndrome.

Synthesis of a sulfur-containing amino acid under simulated prebiotic conditions.

Ultraviolet irradiation of an aqueous solution of ammonium thiocyanate produces the sulfur-containing amino acid methionine. Synthesis of this class of biocompound fills another important gap in development of an overall picture of how prebiological chemistry may have evolved on primitive Earth.