Estimates of Fecundabiity.

It is informed that recent attempts to estimate the probability of pregnancy resulting from a single act of coitus and the length of the fertile period have depended on estimates of the mean fecundability of groups of married women not using contraceptive techniques. There are some points to note about fecundability estimates derived from conception delays: first, it is essential to ascertain a representative sample of women and second, cognisance must be taken of those matings which, although potentially fertile, have not produced a recognizable pregnancy. If they are ignored, fecundability will be overestimated. On the other hand, it seems proper to try to eliminate all women who are absolutely sterile from these considerations. Non-contraceptors have consistently yielded higher estimates even in the case of first pregnancies, and the reasons for this are not entirely clear. It is opined that there are a number of difficulties are associated with estimating fecundability from conception delay.