Is a Mother’s Role in Pregnancy as Host or Hostess?

Refuting the parasite argument for abortion

by Dr. Kaia Kloster on May 13, 2022
Also available in Español

You have probably heard the news already, but rumor has it that the Supreme Court is poised to overturn the highly controversial 1973 court ruling that legalized abortion nationwide—the infamous Roe v. Wade. Public response to the recent leak of a draft opinion has included shock, outrage, and jubilation—depending on where people stand on the issue. Indeed, there are few other issues that energize and polarize the way the issue of abortion does. Pro-abortion activists have taken to the streets, politicians rush to leverage this information to their advantage in mid-term elections, and pro-life entities are prepared to introduce bills and pass legislation in support of its long-awaited abolition.

As is so often the case in our world today, truth can be difficult to discern amid the chaos.

Emotions run high and conversations become heated. Opinions, accusations, and justifications are flung from one side to the other—civility and decorum often left by the wayside. As is so often the case in our world today, truth can be difficult to discern amid the chaos. One argument that has surfaced (perhaps more accurately, re-surfaced) in the pro-abortion camp is the idea that the unborn baby in the womb is merely a parasite, taking what it needs at the expense of the mother.1 As a Christian who holds firmly to the belief that every human life is fearfully and wonderfully made in the image of God and has value from the moment of fertilization, likening a baby to a tapeworm elicits a pretty visceral response! Yet, without resorting to flinging . . . let’s take a closer look at what they posit.

Defining Parasitism

In all honesty, the case can be settled quite simply by looking at the biological definition of a parasite. Parasitism is generally categorized as a form of symbiosis, which is defined as a close, long-term association between organisms of different species.2 A parasite, specifically, is an organism that lives in or on an organism of another species (the host) and benefits by deriving nutrients at the other's expense.3

Since both definitions clearly define the relationship between organisms from different species, we can respond simply and emphatically that an unborn baby is not a parasite. However, recognizing that there are other definitions of parasite that have been used in this debate and realizing that we may need to be prepared with a more comprehensive response, let’s take a little deeper look at the physiological level.

Definitions clearly define the relationship between organisms from different species, [so] we can respond simply and emphatically that an unborn baby is not a parasite.

A parasite comes from outside the body and invades, in one way or another, to obtain what is needed from the host. Our body sees the parasite as a foreign invader and mounts a defense to try to fend it off. While many parasites have unique ways to try to evade our immune system, once detected, an amazingly complex cascade of events happens inside our bodies to restrict or eradicate the invader. The first line of defense involves what is known as innate immunity, which is a nonspecific mechanism mediated by numerous cells, including phagocytes, T cells, mast cells, basophils, and eosinophils, as well as the complement system.4

The innate immune system often fails to adequately control the parasitic invasion, and, in that case, adaptive immunity develops. The cells of the adaptive immune system include T cells, which are activated through the interaction with antigen-presenting cells (APCs), and B cells.5 This process of training various cells of the immune system to identify a particular foreign invader, mount an effective defense strategy, and remember that invader in order to be even more prepared in the case of future invasions is nothing short of amazing. It’s like special ops in the military—they are specially trained fighting units prepared to combat targeted enemies that pose a specific threat. In this case, the enemies are parasites that threaten our bodies.

Designed to Nurture

In light of this, it is interesting to consider the case of pregnancy, the presence of a child living within the womb of the mother, as an example of a parasite. While it does indeed live within the mother and draws its nutrients from her, which could appear “parasitic,” the body’s response is very different. Indeed, as I considered this, I couldn’t help but think the developing child is treated far more like a guest than an invader!

Let’s pause for a moment to think about the ways in which a good hostess welcomes and cares for her guest. If you are expecting company, you prepare in anticipation of their arrival—cleaning, washing the bedding, buying groceries. You unlock the door and disengage any security system so they have access into your home. You create a welcoming environment for them. You prepare meals and clean up afterward. And, as we all know, there may come a time when a guest has overstayed their welcome so you may begin to make things a little less comfortable to encourage their departure. If worse comes to worse, you kick them out!

We have actually been designed to welcome a baby as a guest! Our body makes preparations before its arrival—even prior to conception.

How then does this compare to a woman’s body and pregnancy? We have actually been designed to welcome a baby as a guest! Our body makes preparations before its arrival—even prior to conception.

Each month, the lining of the uterine wall is thickened and prepared for the possible arrival and implantation of a fertilized egg. The woman’s body “turns off” the security system to allow a fertilized egg with foreign genetic material to have safe access. Regulatory T cells (Tregs), which are a specialized subpopulation of T cells that act to suppress the immune response, are accumulated and activated in the uterus each month following the hormonal changes associated with the menstrual cycle. Even more, these protective regulatory cells are temporarily recruited to the uterus after intercourse just in case it could lead to pregnancy. If fertilization does occur, these same immune cells play a critical role in protecting the embryo and preventing rejection by Mom’s immune system—despite being genetically different due to the paternal genes present.6 In essence, the embryo is not attacked but rather welcomed into a cozy place that has been prepared.

The placenta is an incredible organ derived from fetal tissue. While the baby’s and the mother’s blood supply do not directly mix, there is an intricate interface with the mother’s uterine wall whereby they can make exchanges. The baby is connected to the placenta via the umbilical cord, which not only carries things like water, glucose, and vitamins to the developing fetus and supplies it with oxygen but also carries away waste products, including urea, uric acid, and bilirubin, to be disposed of through the maternal blood circulation. It’s a buffet and a public restroom!

As with any guest, there comes a time when they just need to leave! Typically (and hopefully), when the baby is fully developed, the birthing process begins. The earliest contractions cause the cervix to open (dilate) and soften as well as shorten and thin (efface) to allow the baby to move into the birth canal. The baby is delivered during active labor, followed by the delivery of the placenta. The guest is shown out the door, and their luggage is tossed out behind them!

To summarize, the mother’s body’s response to a parasitic infection is completely different than its response to pregnancy. There is no anticipation or accommodation when it comes to parasitism. Yet during pregnancy, the human immune system mounts a complex mechanism that prepares the uterus, ensures the maintenance of immune tolerance to the baby, and allows a steady supply of nutrients and oxygen for proper growth and development.7 So while the analogy of the parasite is much like that of war, the analogy in the case of an unborn baby is like that of hospitality. The body fights one and welcomes the other. A mother, then, serves not as a host . . . but a hostess!

The mother’s body’s response to a parasitic infection is completely different than its response to pregnancy.

Discerning Truth

So, while untrue, it is not without intention that the pro-abortion side has perpetuated this parasite argument. It dehumanizes and devalues the life of the unborn child. It justifies to them a woman’s decision to rid herself of a “parasite.” Yet, biologically speaking, there is no basis for that argument. The developing child is not an invader: it is the woman’s offspring. Parasitism and procreation are very different things. Discerning truth is important as we form our position and engage with culture on this issue. Hopefully, this helps to bring some clarity.

There are surely additional scientific, and perhaps even more convincing arguments, to make, and yet perhaps one of the most convincing to me remains that of the human emotional response. I'm sure you have known a mother who grieves the loss of a stillborn. Perhaps this is you or someone you love. The so-called “unwanted” children—victims of the infamous Roe v. Wade decision—are surely grieved at some time by someone. Perhaps this is you or someone you love. But I have yet to meet anyone who has grieved the loss of a tapeworm.

You see, in our mind we know an unborn baby is not a parasite. But even more importantly, God’s Word makes it clear that the unborn, as humans, have been created in the image of God (Genesis 1:26–27) and are known by him (Jeremiah 1:5). And as image-bearers ourselves, we sense the terrible wrong of destroying other image-bearers, particularly in their most helpless state (Genesis 9:6; Psalm 10:13-14; Proverbs 6:17). To deny this is to deny God himself (Romans 1:28).

Working for Christ

I would be remiss to close without addressing some additional points regarding the most controversial of issues. While the overturning of Roe v. Wade will certainly be a victory for the pro-life movement, the battle will not be won here—for morality cannot be legislated. Roe v. Wade may be overturned, and pro-life states may pass anti-abortion legislation, but women who still believe abortion is a viable solution will simply find their answer in another state, through abortifacient pills delivered to their doorstep or through perhaps even riskier, often barbaric, procedures. No, the battle rages on for the hearts and minds of unbelievers. For the Holy Spirit alone will bring the conviction necessary to change hearts.

As Christians in this battle, we must continue to fight the good fight! We must continue to share the good news with those who find themselves in seemingly hopeless situations. As Christians, we must not just point our fingers at those who find themselves in these situations: we must be willing to open our hearts, and even our homes, to support these women and their children, praying they choose life. Will we walk with the single mom left alone to support her children? Will we adopt the children they may be willing to carry but not parent? Will we find it in our hearts to love rather than judge? Because that and prayer are what will bring the radical change that is so needed in our nation today. Let us uphold the authority of God’s Word—and do so in love!

A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. By this all people will know that you are my disciples, if you have love for one another. (John 13:34–35)


  1. Judith Jarvis Thomson, “A Defense of Abortion,” Philosophy & Public Affairs, (1971): 47–66.
  2. “Symbiosis,” Biology Online Dictionary, accessed May 11, 2022,
  3. “Parasite,” Oxford Languages Dictionary, accessed May 11, 2022.
  4. R. Warrington et al., “An introduction to immunology and immunopathology,” Allergy, Asthma & Clinical Immunology 7, supplement 1 (November 2011): S1,
  5. F. A. Bonilla and H. C. Oettgen, “Adaptive immunity,” Journal of Allergy and Clinical Immunology 125, supplement 2 (February 2010): S33–S40,
  6. “An embryo, not a parasite,” Options for Pregnancy, accessed May 11, 2022,
  7. Maria Grazia Ruocco, et al., "Regulatory T-cells in pregnancy: historical perspective, state of the art, and burning questions,” Frontiers in Immunology, Frontiers, no. 5 (August 2014): 389,


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