>     I have a client that is nursing her nine month old infant.  The
>     mother's periods had resumed, but they have now stopped.  The obvious
>     answer would be a pregnancy, however, the baby has started to nurse
>     again every 2 hours during the night - would this increase in nursing
>     cause a delay in her periods when the baby is now 9 months old?  We
>     thought that this might be the reason but we are looking for more
>     scientific data, to agree or dispute with our theory.  She has no
>     other signs or symptoms of pregnancy.


Officially, there is no "scientific data" to answer the question of whether
the return to fertility post-partum is a one-way street, or can slip and
slide backwards towards no fertility if the frequency of nursing increases.

Anecdotally, last year I collected over 50 stories from individual women
about this phenomenon -- it is well known among nursing mothers, even though
the data have never been officially collected and studied.  In my own case,
with my last child, he started day care for 6 hours a day at 12.5 months
(September) , and I had my first postpartum period at 13.5 months (October)
and another in November.  I then had 4 weeks off between semesters, from
mid-December to mid-January, and had no period either in December or
January, as he was with me more and nursed more.  Once he went back to day
care in mid-January, my periods returned again.  By the end of that May,
even though he was back with me full time for the summer, my periods
continued regularly.  He nursed until he was 5.5 years old.

Thus, although there is no "scientific data" available, I think you can
reassure this mother than her son's increased frequency of nursing is
responsible for the disappearance of her menstrual periods.

Katherine A. Dettwyler, Ph.D.
Associate Professor of Anthropology and Nutrition
Texas A&M University