Helminthic therapy and fertility

A paper published in 2015 claimed to have discovered a link between infection with “hookworms” and both delayed first pregnancy and extended inter-birth intervals.

2015 Nov Helminth infection, fecundity, and age of first pregnancy in women -- Full text | PDF

Not surprisingly, this finding alarmed some women who are self-treating with therapeutic helminths, especially those using hookworms. However, there are a number of issues with this paper.

The study was carried out in an Amazonian lowland population in Bolivia, so the subjects had very different backgrounds, lifestyles and environment from Western populations.

The worm burdens of these forager-horticulturalists are not quantified. If they were large, their effects would have been significantly different from those experienced by Westerners hosting small, “therapeutic” numbers of worms.

The species of hookworm is not specified, even though there are significant differences between the two types of hookworm, Ancylostoma duodenale (AD) and Necator americanus (NA). These differences include the fact that AD draws almost 10 times more blood while feeding than NA does. The fact that the researchers observed reduced body mass index and lower haemoglobin in the women infected by “hookworms” suggests that these subjects were likely to have been hosting AD, whereas the only hookworm species used in helminthic therapy is NA.

Commentators have raised several further issues in relation to this paper.

There is no evidence of lowered fertility in non-human animals infected by helminths, in spite of the fact that this is something that could reasonably have been expected to be observed by veterinarians and owners of animals.

There is no evidence of prior human epidemiology indicating such a lowered fertility connection in the absence of anaemia and/or worm-induced nutritional deprivation.

A reduction in fertility does not make good evolutionary sense, because any worm that produces this effect would be reducing its own farm stock.

Fortunately, for those who are concerned by this paper, the evidence from helminthic therapy users is that not only does self-treatment with NA and other therapeutic helminths not reduce fertility, but it may actually increase it.

I got pregnant straight away with no problems while hosting. (Link expired)

I got pregnant 4 times while hosting whipworm and hookworm. [1]

I had my first "sticky" pregnancy hosting NA… "sticky" means I did not miscarry for the first time. I had lost 3 pregnancies before hosting NA. I believe NA calmed my immune system, which in turn made my body more able to support a pregnancy. It's hard to know what exactly causes a miscarriage. Could have been my "advanced maternal age", could have been a genetic problem with the fetus, etc. NA have made me feel generally more in balance and healthy, and I needed to be healthy to support a pregnancy. [2] [3]

I conceived on the first try last October at age 37 while hosting NA and taking TSO. I had been on NA for a year and a half, and TSO for about 3 months. So helminths certainly didn't hinder my fertility at all, and perhaps helped considering my age and my health issues. I am currently having a very healthy pregnancy with the baby looking healthy and perfect at my 20 week anatomy scan. (Links expired)

I’ve got worms since June 2013. Two months later I got pregnant on the first try -- I did an ovulation-test, which worked very well. Second time, after I had 4 doses of NA and one very early miscarriage, I also got pregnant thanks to an ovulation-test. N=2 of course, but I can only say that conceiving went extremely easy for us, old parents (I'm 42, boyfriend is 47). The way I see it: the healthier I feel, the better I'm able to tolerate a pregnancy. (Link expired)

Before I started NA my menstrual cycle was becoming inconsistent and I had stopped using birth control for several years as it seemed that I was infertile. Post NA. My menstrual cycle is regular to the day. And my fertility has improved. I have experienced 2 miscarriages while on it. Thus able to conceive. I continue to struggle with a “luteal phase defect.” Nonetheless, my cycle and fertility have improved significantly since I started NA. [4]

After enduring almost five years of unsuccessful fertility treatment, an aspiring mother took a break and began hosting hookworms. Seven months after this, she resumed the use of assisted reproductive technology (ART), this time opting for donor insemination with double donation, and the first ultrasound revealed a beating heart! Five months into the pregnancy, she topped up her hookworm colony with a view to making her child's immune system more resilient. [5] (In French)

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