http://www.l4l.org/library/notparas.html@Joel96 1) The definition of a parasitc relationship as necessarily heterospecific is overly restrictive, as it excludes the few homospecific relationships which do fit the core definition of parasitism, such as cancerous or tumoral cells and narcomedusae. Most parasitic relationships are heterospecific but if a definition excludes relationships which are also sensibly classified as parasitic, it needs reworking.
2) The other gamete required for conception comes from an outside source.
3) The fetus is generally harmful. It causes a whole host of side effects such as
Nausea.
Constipation.
Sore boobs.
Vomiting and morning sickness.
Indigestion and heartburn.
Braxton Hicks.
Depression.
Anxiety.
Detrimental emotion changes due to the fetus pumping the mother full of hormones.
Fatigue.
Bloating.
Insomnia.
Pressure on the bladder leading to increased urination.
And it can cause and be involved in some conditions, like
Hyperemesis gravidarum
Temporary and permanent injury to back
Severe scarring requiring later surgery (especially after additional pregnancies)
Dropped (prolapsed) uterus (especially after additional pregnancies, and other pelvic floor weaknesses -- 11% of women, including cystocele, rectocele, and enterocele)
Pre-eclampsia (edema and hypertension, the most common complication of pregnancy, associated with eclampsia, and affecting 7 - 10% of pregnancies)
Eclampsia (convulsions, coma during pregnancy or labor, high risk of death)
Gestational diabetes
Placenta previa
Anemia (which can be life-threatening)
Thrombocytopenic purpura
Severe cramping
Embolism (blood clots)
Medical disability requiring full bed rest (frequently ordered during part of many pregnancies varying from days to months for health of either mother or baby)
Diastasis recti, also torn abdominal muscles
Mitral valve stenosis (most common cardiac complication)
Serious infection and disease (e.g. increased risk of tuberculosis)
Hormonal imbalance
Ectopic pregnancy (risk of death)
Broken bones (ribcage, "tail bone" )
Hemorrhage and numerous other complications of delivery
Refractory gastroesophageal reflux disease
Aggravation of pre-pregnancy diseases and conditions (e.g. epilepsy is present in .5% of pregnant women, and the pregnancy alters drug metabolism and treatment prospects all the while it increases the number and frequency of seizures)
Severe post-partum depression and psychosis
Research now indicates a possible link between ovarian cancer and female fertility treatments, including "egg harvesting" from infertile women and donors
Research also now indicates correlations between lower breast cancer survival rates and proximity in time to onset of cancer of last pregnancy
Research also indicates a correlation between having six or more pregnancies and a risk of coronary and cardiovascular disease
From
https://www.dailykos.com/story/2012/4/15/1082439/-The-fetus-is-a-parasiteIt's partially an opinion piece, so I cleaned the reasoning up a bit.
4) The human embryo burrows into the endometrium to gain *direct* access to the blood vessels.
5) The endometrium does cut off embryos from the host - it's only by virtue of aggression and strength this defence is overcome. Also, there are competing biological systems here - the immune system recognises a parasite, but procreation is essential for successful organisms so the hemochorial placenta is a way around that. Still, the amniotic sac is still cutting off the fetus. It's like building a giant wall on a border then having one door (placenta). There's not a complete cut off, but it's still cut off that.
6) This point even shows the mother does have an immune response to the fetus, but the fetus has evolved defenses against it. Lots of parasites evolve defenses against their host's response too. The increased chance for homosexuality with younger brothers also indicates the mother does attack the fetus - and gets better with it at each pregnancy.
7) The woman is definitely weakened by the presence of the fetus - there's a reason pregnant women are advised not to do heavy lifting. Also, lots of parasites are completely unrelated to the reproductive system. If you acknowledge reproductive capacity in terms of ability to conceive offspring and also in terms of ability to conceive *healthy* offspring (which would sensible since we're a K-selected species), the biological stress and low mass of babies after repeat pregnancies shows fetuses damage reproductive capacity.
8) Remaining with one host for life is not central to the definition of parasite. Lots of parasites actually move between hosts, so this is an invalid point.
The fetus-mother relationship is commensal at best and if you're an optimist, but parasitic if you're a realist.