SUPRAPHYSIOLOGICAL SERUM RELAXIN CONCENTRATION DURING PREGNANCY ACHIEVED BY IN-VITRO-FERTILIZATION IS STRONGLY CORRELATED TO THE NUMBER OF GROWING FOLLICLES IN THE TREATMENT CYCLE

In order to analyse the relationship between tile ovarian response to stimulation in in-vitro fertilization (IVF) treatment cycles and relax in concentrations during subsequent pregnancies, 31 healthy women preg nant after IVF treatment were studied prospectively. The maximum numbe r of follicles observed from day -4 to day -2 in relation to ovum retr ieval and the number of oocytes recovered mere recorded, In addition, blood samples were drawn in the follicular phase, the luteal phase, ea rly pregnancy and at gestational weeks 12, 16, 20, 27 and 35 to assess oestradiol, progesterone, human chorionic gonadotrophin and relaxin. The maximum numbers (mean +/- SEM) of follicles observed and oocytes r ecovered were 9.0 +/- 0.6 and 6.1 +/- 0.5 respectively. The supraphysi ological mean relaxin values were strongly correlated to the maximum n umber of follicles observed (r = 0.72. P < 0.0001) and the number of o ocytes recovered (r = 0.63, P < 0.0001), indicating that the source of increased relaxin production during IVF pregnancy might be the ovary, These results are supported by experimental data, In the present stud y, the occurrence of multiple pregnancy was not associated with higher relaxin concentrations, which is further support for the hypothesis t hat the ovary is the main source of serum relaxin.