A Brief Physiology of Conception, Abortion, and Labor

This post is a departure from my typical history posts, but I have had people asking a lot of questions and what could be more important to our practice of domestic medicine then having a thorough understanding of this physiology and how various agents interact with our reproductive cycle? Our modern advantage is having a more accurate view of how our bodies work than our ancestors had, as I have hopefully illustrated in previous posts.

This post is going to be about conception and the expulsion of the products of conception from the uterus which usually happens in one of two ways – abortion or labor.   I will try to keep this as brief as I can, while still getting across key points about moments when using herbal adjuncts might be appropriate or when they are being used inappropriately.

I am assuming most of my readers are people who have already been introduced to the human reproductive system but if it’s been a long time since school, here’s a blog post to catch you up.  There’s one point I want to make because of the You Tube video at the end.  There is more recent data that leads researchers to believe that thickening cervical mucus is a long-term effect of levonorgestrel IUDs that does not occur with short term use. What this boils down to is that these types of emergency contraception are only useful if taken before ovulation.

Levonorgestrel (Plan B) is a type of hormone called a progestin. It binds to progesterone and androgen receptors and slows the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus which works to delay the release of an egg from the ovaries for up to 72 hours. It is unlikely to work if you have already ovulated for the month.[1]

Ulipristal acetate (Ella) is a progesterone receptor modulator. It inhibits ovulation and may have some impact on the rhythm of cilia movement in the fallopian tube which interferes with the movement of the oocyte (unfertilized egg) or zygote (fertilized egg) being carried by the cilia through the fallopian tubes to the uterus, but there is no indication that in has any effect on implantation.[2] It is not a prostaglandin.

I suppose I should start with talking about prostaglandins.  The human body produces many types of prostaglandins.  Many prostaglandins play a role in acute and chronic inflammation. The prostaglandin thromboxane contracts muscles in the walls of blood vessels and stimulates the formation of blood clots.  When the danger of bleeding out is past, prostacyclin (another prostaglandin) relaxes them. There are also natural and synthetic substances that interfere with the production of prostaglandins via various mechanisms.  For example, aspirin blocks the production of thromboxane and so can be used to prevent unwanted blood clotting in patients with heart disease

Prostaglandins are very active in a person who is in their menstruating years. Every month the epithelial mucosal membrane lining of the uterus remodels itself into what is called the decidua. The decidua contains glands, immune cells, blood, lymph vessels, and decidual stromal cells (DSCs) that support implantation and pregnancy. The decidua relies almost entirely on the body producing sustained levels of progesterone, to remain intact. When progesterone levels fall, this triggers an inflammatory cascade in the decidua that activates leukocytes that destroy the tissue to the point that shedding of the lining occurs. This is menstruation. Prostaglandins also trigger myometrial muscles to contract in a way that expels this shedding epithelial lining.

“PGF2 alpha vasoconstricts the endometrial vessels during menstruation and contracts the smooth muscle of the myometrium. PGE2 vasodilates the vessels of the endometrium, and PGI2 relaxes smooth muscle, vasodilates the vessels of the myometrium and inhibits thrombocyte aggregation.”[3]  

These prostaglandins are often what result in the discomforts of menstruation. PGF2 can enter the blood stream and cause other smooth muscles to contract.  This is what leads to gas, bloating and changes in bowel habits that happen during menstruation. Carminatives are herbs, such as mint and fennel are herbs that specifically relax contracted GI tissue and may be useful here.

The higher the level PGF2 α that you naturally produce, the more likely you are to have severe menstrual cramps. NSAIDs have been shown to reduce myometrial activity by inhibiting prostaglandin synthesis.[4] If you are one of my students you know that this is because they block the action of cyclooxygenase enzymes, and that there are herbal adjuncts that have similar effects on these enzymes. Humulene from Humulus lupulus strobiles (hops) is a highly effective Cox-2 inhibitor. In one DBRCT a hops extract demonstrated a similar effect as 400mg of ibuprofen along with Cox-1 sparing activity[5] which basically means it has a comparable anti-inflammatory effect without the side-effects.

Implantation of a zygote usually occurs 8-9 days after conception. The gestational sac will grow, the embryo will form, and the placenta will produce hormones including human chorionic gonadotropin (hCG) which signals the ovaries to keep producing progesterone for at least the first 8-10 weeks of the pregnancy. This also triggers an immune process that keeps the body from rejecting the embryonic tissue.  If you read that an herbal preparation prevents implantation, it is most likely implying that it does something to block/inhibit the progesterone supply sustaining the decidua which makes the decidua uninhabitable for an embryo.

When the chromosomes in the sperm and egg do not line up properly to create a viable embryo, an anembryonic pregnancy (blighted ovum) occurs.  The gestational sac develops, and you will test positive on a pregnancy test.  The placenta may form in the sac, but without a viable embryo it cannot become established.  Somewhere between 8-12 weeks, the ‘luteo-placental shift’ occurs.  At this point an established placenta will produce progesterone. If this does not happen progesterone levels fall, and the gestational sac and other products of conception will (usually) eventually be shed with the lining.  

Some researchers believe that as many as one in four pregnancies end this way. Most spontaneous abortions occur in the first trimester. If it were not for our advanced modern day pregnancy tests and ultrasounds, these anembryonic pregnancies would just be thought to be delayed menstruation.  This happened so often in the past that physicians thought that some women only menstruated every few months. 

In the first trimester of pregnancy (up to 77 days) chemical abortions can be done by administering mifepristone (formally RU-486) which is a progesterone antagonist that blocks progesterone produced by the ovaries from being able to sustain the lining of the uterus followed by misoprostal (Cytotec) which is a prostaglandin that signals the uterus to begin contracting and leads to the subsequent shedding of the lining.   Studies show that mifepristone by itself is less likely to be effective and there is an increased risk of incomplete abortion. When taking both pills fails, it is likely because the conception date was wrong, and the pregnancy has progressed past the luteo-placental shift. At this point a surgical abortion is necessary.

As the embryo progresses, fetal tissue and the placenta produce prostaglandins which stimulate the uterus to develop more receptor sites for oxytocin.  This is important to understand. The further along the pregnancy the more sensitive the uterus is to oxytocin.  Oxytocin is a hormone that causes uterine muscles to contract and also increases production of prostaglandins that cause contractions. 

Giving someone an oxytocic agent early in pregnancy is unlikely to be an effective means of aborting an embryo. It’s not likely to produce strong enough contractions which would increase the risk of an incomplete abortion.   This requires further medical care and could result in the necessity of surgical management with dilation and curettage. Complications of incomplete abortion, may include sepsis due to the retention of products of conception, hemorrhagic shock from loss of blood, uterine rupture, or cervical shock from cervical stimulation by products of conception stuck in the cervix.

All the new receptors mentioned above contribute to the much stronger myometrial contractions necessary for childbirth but so do rising oxytocin levels. Illnesses that result in decreased blood volume such as dehydration, food poisoning, or a virus that causes diarrhea may artificially elevate the concentration of oxytocin in the blood, and this can trigger stronger contractions and pre-term labor.

Purgatives and emetics that midwives suggest for starting a post-term labor, such as drinking castor oil, work in part this way by reducing your blood volume and in part because spasmodic peristalsis in the GI tract is triggered by prostaglandins that contract smooth muscle in the intestines. Those prostaglandins can in turn get into your blood stream and may trigger contractions in your uterus. The thing is they don’t always work and it’s a miserable way to begin labor even if they do.

Normally, oxytocin is released in bursts during labor and then relaxin, a hormone produced in the decidua and placenta during pregnancy, suppresses uterine contractions in between oxytocin bursts and relaxes pelvic connective tissue.  This is what accounts for the break between contractions in labor.

Having these extra receptors and more oxytocin still does not ensure progression. Part of the way you can tell labor is imminent is that prostaglandins cause changes in the cervix prior to active labor.  It softens, effaces, and dilates. It is not uncommon for a woman to be 2-3 cm dilated for the last month or so of pregnancy.

If the cervix isn’t soft enough to dilate, labor might fail to progress, resulting in the need for a c-section.  This is why they don’t just shoot you with Pitocin to start labor. In my history post you will see that this is something that physicians have known since Hippocrates wrote On Diseases of Women. Many agents that were thought to hasten labor were applied as suppositories near or in the mouth of the cervix.

Today when they induce labor in the hospital, they first apply cervix ripeners such as dinoprostone or misoprostol (Cytotec) to the cervix to soften the collagenase present and allow it to dilate. Sometimes the vasodilation of the endometrium vessels will trigger contractions in a full-term pregnancy, but not always.  If necessary, they follow-up with Pitocin (synthetic oxytocin), because at this point all those oxytocin receptors are present.

I want to end this by briefly talking about how stress affects menstruation and labor.  Stress and/or fear stimulate the release of adrenalin and adrenocorticotropic hormones which will in term inhibit the amount of oxytocin released by the body and consequently the contraction of the uterus by the myometrial muscles.[6] This can cause delayed menstruation, post-term pregnancy, or stall the progression of labor.  

There are herbal remedies that midwives have used for centuries to poke a post-term pregnancy or to jumpstart a stalled labor. Some are simply smooth muscle relaxants that act as calcium channel blockers in the smooth muscle of the myometrium. Even a warm hot water bottle might help relax tense muscles.

Agents that reduce the levels of adrenalin and noradrenalin via stimulation of the parasympathetic nervous system allow muscles to relax and normal oxytocin production to occur. Some herbal preparations that are “oxytocic” are simply cholinergic herbs that that mimic the action of acetylcholine (ACh) directly stimulating cholinergic receptors [nicotinic and muscarinic] which in turn stimulates the parasympathetic nervous system or indirect acting parasympathomimetic nervines that promote the release of ACh or are acetylcholinesterase inhibitors. I would place hydroethanolic extracts of wormwood/mugwort, lemon balm, and angelica which act as mild nicotinic receptor agonists in this group.[7] Chamomile also has this effect There’s even a tiny bit of actual human trial clinical data to support the use of chamomile here.[11]  

Other agents may mimic oxytocin in the body in its capacity to stimulate the release of prostaglandins.  The allocryptopine in Eschscholzia californica (California poppy) is a known oxytocic which is why the herb is contraindicated in pregnancy[8] as is the alkaloid stachydrine in Leonurus cardiaca (motherwort).[9] Based on the success of preliminary research, Chinese physicians have experimented with successfully using a combination of motherwort and Pitocin to better control post-partum hemorrhage.[10]

It’s honestly kind of outside of the scope of domestic medicine which is more empiric in nature for me to be talking about this.   It takes a lot of training to have a handle on why we think certain herbs work the way they do and even then, some of it is just theory. 

The point is that none of the mechanisms listed above are likely to start labor-quality contractions until later in pregnancy when sufficient oxytocin receptors are present, This information might be useful for the person who’s experiencing a delayed menstrual cycle due to midterm stress, or some of the doulas and midwives out there.

I have had many, many women ask me to help them because they were past their due date and worried about being forced to induce.  It’s an unfortunate side effect of too much medical intervention in labor and delivery. I want to address that here and we will move on to the history of early interventions in the next posts.

I have seen too many overdue women take preparations, against my advice, which are quite possibly toxic to both themselves or their unborn child in the large doses they consume, and they didn’t work at all. I have seen modern midwives recommend things that would have prompted my great-grandmother to take them by the scruff of their ear and put them back to work washing the laundry after births, until they learned some prudence.

It’s really not as easy to evict the fetus as the Internet would have you believe. The only method I would be willing to say I would suggest as consistently starting post-term labor that is safe for both mother and child is a process involving a relaxing beverage (chamomile tea), application of semen (which contains prostaglandin PGE2) to the cervix, stimulating oxytocin naturally (massages are nice), and then walking. It usually takes about three cycles, and even if it does not work it is a much more pleasant way to spend time than with severe cramps and diarrhea.


[1] Endler, M., R. H. W. Li, and K. Gemzell Danielsson. ‘Effect of Levonorgestrel Emergency Contraception on Implantation and Fertility: A Review’. Contraception 109 (1 May 2022): 8–18. https://doi.org/10.1016/j.contraception.2022.01.006.
[2] Li, Hang Wun Raymond, Michele Resche-Rigon, Indrani C. Bagchi, Kristina Gemzell-Danielsson, and Anna Glasier. ‘Does Ulipristal Acetate Emergency Contraception (Ella®) Interfere with Implantation?’ Contraception 100, no. 5 (1 November 2019): 386–90. https://doi.org/10.1016/j.contraception.2019.07.140.+
[3]Jensen DV, Andersen KB, Wagner G. Prostaglandins in the menstrual cycle of women. A review. Dan Med Bull. 1987 Jun;34(3):178-82. PMID: 3297513.
[4]. Zahradnik HP, Hanjalic-Beck A, Groth K. Nonsteroidal anti-inflammatory drugs and hormonal contraceptives for pain relief from dysmenorrhea: a review. Contraception. 2010;81(3):185-196. doi:10.1016/j.contraception.2009.09.014
[5] Lemay M, Murray MA, Davies A, Roh-Schmidt H, Randolph RK. In vitro and ex vivo cyclooxygenase inhibition by a hops extract. Asia Pacific journal of clinical nutrition 2004; 13(Suppl): S110
[6] Nabb, Mary T. Mc, Linda Kimber, Anne Haines, and Christine McCourt. ‘Does Regular Massage from Late Pregnancy to Birth Decrease Maternal Pain Perception during Labour and Birth?–A Feasibility Study to Investigate a Programme of Massage, Controlled Breathing and Visualization, from 36 Weeks of Pregnancy until Birth’. Complementary Therapies in Clinical Practice 12, no. 3 (August 2006): 222–31. https://doi.org/10.1016/j.ctcp.2005.12.006.
[7] Perry, Nicolette, Gudrun Court, Natalie Bidet, Jenny Court, and Elaine Perry. “European Herbs with Cholinergic Activities: Potential in Dementia Therapy.” International Journal of Geriatric Psychiatry 11, no. 12 (December 1996): 1063–69.
[8] Abascal, K., & Yarnell, E. (2004). Nervine Herbs for Treating Anxiety. Alternative and Complementary Therapies, 10(6), 309–315.
[9] Chen ZS, Chen CX, Kwan CY. Leonurine, an alkaloid isolated from Leonurus artemesia induces contraction in mouse uterine smooth but relaxation in vascular smooth muscle of rat portal vein. Biomed Res 2000;11:209–12.
[10] Liu, Wei, Shihong Ma, Wenjing Pan, and Wenhua Tan. ‘Combination of Motherwort Injection and Oxytocin for the Prevention of Postpartum Hemorrhage after Cesarean Section’. The Journal of Maternal-Fetal & Neonatal Medicine, 28 September 2015, 1–4. https://doi.org/10.3109/14767058.2015.1090425.

Published by Stephany Riley Hoffelt

If you want to read more about me, it's on the website www.domestic-medicine.com

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