Coitus-Induced Ovulation and Its Implications for Estimates of Some Reproductive Parameters

Abstract

It is estimated here that, at the time of conception, the mean coital rate of young women who subsequently bear DZ twins is about 6% higher than that of the general population of young married women. This differential seems too small to account wholly for the greater promptness in conceiving DZ twins. Accordingly, it is suggested that coital rate is associated with DZ twinning in two ways. The major link seems to be indirect and mediated by erotic response which causes an increase in gonadotrophin levels and thus in double ovulation. In a minority of cases, frequent coitus may give rise to DZ twins via superfecundation, but it seems that, in human beings, the corpus luteum of one ovum will usually inhibit fertilization of any further ova after a short interval. The evidence presented here, though indirect, seems to suggest that, under particularly erotic conditions, double ovulation is sometimes induced. It seems reasonable to infer that coitus also occasionally provokes or accelerates single ovulations, thus impugning some rhythm methods of contraception. But there seems no very good evidence that rape induces ovulation. Some notes are added on the implications of induced ovulation for estimates of fecundability and of the length of the fertile period.

Seasonal variation of livebirths, stillbirths, extramarital births and twin maternities in Switzerland

“…A t l east i n the UK there i s evi dence of greater vol ume of sal es of contracepti ve materi al s i n the summer and the seasonal vari ati on i n sexual offences al so argues that thi s seasonal i ty i s not w hol l y dependent on opportuni ty. 27,28 Data from the USA suggest that l oss of virginity is particularly likely during the summer. 29 In the USA seasonal fl uctuati ons i n coi tal rates have been noted; how ever, shi fti ng the bi rth rates back 40 w eeks to the approxi mate concepti on dates reveal ed no associ ati on w i th the observed coi tal rates.…”

The Incidence of Superfecundation and of Double Paternity in the General Population

“…The first assumption is that if a woman has intercourse with 2 men, she will be equally at risk of conception by each. However, there are reasons for wondering if there may a bias in favour of fecundation by lovers vis-a-vis husbands: a) I have argued that particularly erotic circumstances may sometimes provoke or accelerate ovulations [9] and one might suppose that lovers have an advantage in this regard.…”

“…However, it appeared from these data that a doubling of coital rates very roughly corresponded to an increase of only 25% in the DZ twinning rate. And this was estimated to imply that the mean additional increment in the coital rate of DZ twinbearers over singleton-bearers was of the order of only 6% [9]. DZ twin-bearers are substantially more fecundable than singleton-bearers: and the increment of 6% described seems inadequate to account for this.…”

Coital frequency and twinning

“…Mother's age and number of previous births are positively associated with dizygotic (DZ) twinning (Nylander, 1981), and an association of DZ twinning with coital frequency has also been suggested (James, 1972(James, , 1981(James, , 1984.…”