Hosting helminths during pregnancy is commonplace, with approximately 44 million pregnancies occurring globally each year in women with helminths. 
De-worming during pregnancy is not advantageous and may be harmful
Many medics have advocated de-worming pregnant women to prevent a range of supposed health risks, but studies have found that, where good antenatal care is provided, de-worming produces no benefits in respect of anaemia, birth weight, perinatal mortality, infant mortality or infant response to immunisation.   
Both mother and child benefit when helminths are hosted during pregnancy
Prenatal exposure to parasite antigens impacts on the strength and width of postnatal immune responsiveness without generating aberrant inflammatory immune responses. Neonates not exposed to parasite antigens have inappropriately increased or decreased gene expression profiles. 
Current epidemiological findings suggest that prenatal exposure to helminth infection may have an important effect on the development of the foetal immune response and that this might help prevent the emergence of inflammatory conditions such as allergy. 
Studies from Uganda have shown that hookworm colonisation in pregnant women confers protection against infantile atopic eczema, protection that is abrogated by anthelmintic treatment during pregnancy.   The presence of helminths at delivery has also been shown to be inversely related to infantile eczema, adding further support to the hypothesis that maternal helminth infection protects against this disease. 
Helminth infection in the perinatal period protects children from the neurological damage that can accompany bacterial infections, and this protection extends into adulthood. 
Antenatal maternal helminth infections are associated with modestly increased IgA responses to oral infant vaccines. 
Sepsis, a condition that is hard to recognise and treat, is an increasing cause of complications and death among women in the West, and rates of severe and fatal sepsis during labor and delivery are rising sharply, such that sepsis is now the leading cause of direct maternal death in the UK. 
As a helminth infection counterbalances the exacerbated pro-inflammatory immune responses that occur during sepsis, thus improving survival, it is arguable that the presence of a small colony of therapeutic helminths might actually prevent a woman developing sepsis. 
Hyperemesis gravidarum (HG) is a pregnancy complication characterised by severe nausea, vomiting, weight loss, and possibly dehydration,  which is considered more severe than morning sickness.  In view of the fact that allergy is the most significant condition associated with HG prior to pregnancy  - which suggests a possible allergic or autoimmune component - it is possible that women who are hosting helminths might be less likely to develop HG.
Since helminths control inflammation, commencing helminthic therapy prior to pregnancy might help women who have autoimmune disorders such as colitis to stay healthy during pregnancy,  and help to spare their offspring adverse, inflammation-related effects on brain development, some of which can result in autism-like features.  
Reports by women who hosted small numbers of helminths while pregnant
One woman who examined all the available evidence on the risks and benefits of hosting helminths during pregnancy came to the following conclusion.
And she reported, at a later date,
Someone else, who had previously had two children with severe eosinophilic esophagitis-related food intolerances, maintained a hookworm colony throughout her next pregnancy and delivered a healthy, allergy-free baby. (Expired link)
Other mothers have reported as follows.
Mothers, as well as their babies, can benefit by continuing to host helminths during their pregnancy.
The question of whether to introduce helminths during pregnancy
Notwithstanding the fact that approximately 44 million pregnancies occur globally each year in women who are hosting helminths,  and the many health benefits to be gained by both mother and child as a result of establishing a helminth colony before becoming pregnant, some women are reluctant to commence helminthic therapy for the first time during pregnancy.
If a woman were to start helminthic therapy while pregnant and have a miscarriage, or encounter a problem with the new baby, they, or their healthcare providers, might blame the helminths, and legal action could be taken against whoever supplied them. This has led some helminth providers to decline to supply anyone who is pregnant.
Another provider recommends supervision by a physician during pregnancy.
But one helminth provider who has supplied many thousands of individuals, including many pregnant women, since 1998 without any adverse effects being observed, is confident that their particular organism is safe for use during pregnancy.
Here are quotes from a few of the many women who have inoculated with probiotic helminths during pregnancy, none of whom have reported anything untoward.
Note: if a woman wished to terminate a helminth colony during pregnancy, it had been suggested that it would be best to avoid the use of mebendazole. However, a study in 2016 found no association between exposure to mebendazole at any time during pregnancy and negative birth outcomes. 
Discussion threads about helminths and pregnancy
1. Experiences of pregnancy as a current or recent helminth host. Sept 2013. 
2. A doctor’s concern about a hookworm-hosting pregnant patient. Dec 2016. 
- Helminthic therapy and fertility
- Helminthic therapy and breastfeeding
- Helminthic therapy and children
- Helminthic therapy safety
- Deworming debunked
- Maternal helminth infections and the shaping of offspring immunity
- Calm the immune system, halt premature birth
- Exposure to Parasitic Protists and Helminths Changes the Intestinal Community Structure of Bacterial Communities in a Cohort of Mother-Child Binomials… (The presence of intestinal parasites is linked to strong bacterial microbiota community changes and may also lead to changes in the vertical transmission of bacterial taxa, implying that parasitic colonization may be an important indirect factor in the inheritable features of the human gut microbiome.)