We meet the hydrosalpinx in the box, Salpinx, hydrosalpinx and pyosalpinx, on WebPage 12. Whether present on one side or both sides, a hydrosalpinx spells trouble for getting pregnant -- naturally or with IVF. The reason is complicated but important.

A hydrosalpinx forms when a fallopian tube, damaged from salpingitis, becomes blocked at the outer, fimbrial end, close to ovary. Most hydrosalpinges, however, are not blocked at the inner, uterine end -- they remain in direct communication with the cavity of the uterus, the endometrial cavity. The isthmus of the hydrosalpinx is still open, as is the isthmus of a normal tube.

So what? Well, the problem starts when a dominant f ollicle in either ovary starts producing estradiol -- either naturally or with superovulation. Estradiol causes the isthmus of the fallopian tube to become (temporarily) occluded. Meanwhile estradiol also stimulates the hydrosalpinx to fill up with even more, watery fluid. Ovulation -- or follicle aspiration for egg retrieval -- then takes place and the empty follicle begins to produce progesterone.

As we see on WebPage 3, progesterone prepares the uterus for pregnancy, and does so in many ways. One of these ways, in normal circumstances, is to cause the isthmus of the tubes to relax, admitting to the uterus an embryo previously held up at the ampullary-isthmic junction, about three days after ovulation and fertilization (and the same time that's chosen in IVF programs to deliver IVF embryos to the uterus through the cervix).

The treachery occurs because it's this precise time that the embryo or embryos should be gently held between the front and the back surface of the endometrium. Fluid from the hydrosalpinx then trickles or gushes down through the endometrial cavity, inevitably posing a major threat to successful implantation. Pregnancy is lucky not to fail completely. Miscarriage is common among the implantations that survive the gush.

Remember, a hydrosalpinx affecting just one tube will cause this nasty trap to be set, even if the other tube is completely normal and open.

What to do about it? At the least, the appearance of a previously unknown hydrosalpinx during follicle tracking with commitment to IVF should mean emptying the hydrosalpinx at the same time (and in the same way) that the fluid is collected from the follicles to retrieve the eggs, and maybe repeating this at the embryo transfer. This might not be enough, however. Moreover, aspiration at embryo transfer could cause some bleeding into the tube that might add to the embryo's woes.

In the longer term, and preferably before IVF treatment starts, better options include removing the offending tube or tubes (salpingectomy), opening the tube with a microsurgical salpingostomy, or placing a clip on the tubal isthmus, as described on WebPage 13.