Picking on a single matter such as pregnancy won't affect their opinion.

If I were to attempt to change their mind (I would more likely avoid them), I would instead ask why they thought the holocaust was a hoax, i.e. why so many people believe it's true. If they were to come back with some kind of "illuminati" argument, I would not press any further.

Edit: To add, the single greatest argument against holocaust deniers is quite simply the very detailed records the Nazis made of their plans for genocide and "Lebensraum", the elimination of Jews (among others), as well as very extensive details they recorded as they went about executing these plans.

You probably want to check out the FAQ section at Askhistorians about the Holocaust, and specifically Holocaust Denial and How to Combat It by u/commiespaceinvader.

The TL:DR is that you can engage Holocaust denial arguments, but really can't engage Holocaust Deniers personally, because you're not even going to share the same premise with them as to what constitutes facts. It's very common for Holocaust deniers to pick and harp on a particular detail (it looks like in this case something about camp pregnancies) to claim that the entire Holocaust couldn't have happened. If it wasn't this thing, if you could manage to convince them otherwise (like by, say, pointing out that concentration camps and death camps were different camps), they would just move on to another "anomalous" detail disproving the existence of the Holocaust. When such a person also thinks that Jews control the media and that they're engaged in a global white genocide...how can you even present evidence to challenge their views on the Holocaust? Any such evidence will clearly just be fabricated by this conspiracy and "false" in their mind.

ETA - de-radicalization, especially of people part of or sympathetic to neo-nazi and neofascist movements, is possible, but it's really tricky. It usually requires the person involved to have some sort of disillusionment, and usually it's successful when they can reach out to other people who left the movement. The people who do deradicalization work say that a regular person - if they have the energy to engage - can be empathetic to such people ("What are the reasons that make you feel that way, that make you angry or afraid?"), but this is really difficult work with very uncertain outcomes, and literally it's something that professionals do full time, even then with mixed results. But you won't deradicalize someone by somehow proving the historic facts they think are true are in fact wrong through a debate - usually if anything this actually validates their viewpoints more.

I agree with the earlier comments that any debate with a Holocaust denier is useless and counterproductive, they come from a place of hatred not ignorance. I can however answer the question about pregnancy for your own interest. The best primary source on pregnancy in Auschwitz in my opinion is Dr. Gisella Perl’s memoir of her imprisonment in Auschwitz and her role as a camp physician and underground abortionist. Her memoir categorized most pregnancies in Auschwitz as either occurring due to rape by guards or other prisoners or occurred in women who had been very early in their pregnancies who weren’t identified as pregnant at the Selection and so weren’t immediately sent to the gas. Dr. Perl discovered shortly after she was imprisoned that any women found to be pregnant in the camp were subject to medical torture before being summarily killed, she as a gynecologist was expected to turn any pregnant women over to Mengele and the other Nazi doctors immediately on threat of death. However she chose to resist, making sure that “there would never again be another pregnant woman in Auschwitz”. She took whatever medical supplies she could and performed abortions under cover of darkness saving the lives of possibly hundreds of women. Circumstances regarding pregnancy were different in other scenarios of imprisonment during the Holocaust. In ghettos there was no separation of the sexes so women became pregnant regularly, however many women lost their fertility due to starvation, others attempted to avoid pregnancy because of the increasing violence. Pregnant women would also have been among the first to be deported to killing centers. In death camps where there was a significant selection process (Auschwitz I and Birkenau, and to a lesser extent Majdanek) visibly pregnant women were killed immediately, however women who were very early in their pregnancy may have evaded the selection. In other death camps, as well as sites of mass shooting where all or very nearly all those deported were killed immediately, including pregnant women. In places like concentration camps and labor camps sexualized violence was rampant, though very hard to study, and although many women were infertile due to starvation there were many many women who would have become pregnant while imprisoned in camps through rape, and occasionally due to consensual sex. Jewish women who were discovered to be pregnant would be either killed immediately or sent to a killing center. Women’s bodies are resilient, and though most women imprisoned by the Nazis would have lost their fertility due to starvation, not everyone did. Women who managed to hide their pregnancies may even have given birth in concentration camps, including Auschwitz, though the children did not survive. This is quite graphic but some films of liberation of concentration camps shows the bodies of infants, as well as the bodies of very premature fetuses who may have been stillborn, or possibly delivered after an abortion. Pregnancy was not common in camps, (primarily concentration and forced labor camps but in certain death camps such as Auschwitz Birkenau with a large prisoner population) but it did happen. We know that children were born in camps, there may even have been a handful conceived in them, but these children and very often their mothers as well, did not survive.

“I Was A Doctor in Auschwitz” by Dr. Gisella Perl “The Shawl” by Cynthia Ozick

People like Holocaust deniers dont argue in good faith. Consider whether it is worth your time to do this when it is unlikely that anything will change their mind.

While as others have said arguing with a holocaust denier is somewhat of a fools errand. If you want to do it here's what I would do. A lot of holocaust denial involves nitpicking details of the camps and "just asking questions type denialism" deniers have arguments and "knowledge" or at least think they do about these topics so it's time to do some just asking questions of your own, so say you'll answer her pregnancy question but only if she answers one of your own namely, what happened to the Polish Jews?

Pre-war Poland had about 3 million Jews the vast majority which spoke Yiddish as a first language. Post war Poland had around 240,000 at the highest that's a lot of people missing where did they go? She'll most likely say Isreal well in 1948 Israel had only around 900,000 people, including Arabs previous migrants and migrants from other places. As of now Israel has around 6 million Jews and Poland has virtually none. If those Jews "all went to Israel" then half of all Israeli Jews should be of Polish decent and half of all Israelis should speak Yiddish, however, this is not the case and barely 2% of Israelis can speak Yiddish. That is Ignoring the other communities in Europe particularly in Belarus and Lithuania which also vanished. The numbers absolutely do not add up.

Deniers always tend to deal solely with the camps and gas chambers the part of the holocaust that is in the popular imagination. However, in the academic study of the holocaust the camps are only half of it the other half was on the Eastern front and much less organized if no less genocidal, I've focused on that part for two reasons the first being it's part of an overall picture which is often lost in the minutia these arguments, and the second because I can actually give an informed answer on these topics. I can't give you so much information about the exact running of the camps or gas chambers, though others here certianly can, but I can show that there is a giant hole in Eastern European demographics where the Jews should be. The other thing deniers tend to do is say German and Soviet records are untrustworthy because the Allies tampered with the German records (false) and the Soviets were a totalitarian dictatorship (true) but we have other corroborations for their holocaust records. However, the Poland demographic data undercuts these deneir arguments false as they are because we can show the demographics of Poland using pre-war Polich census data which I've cited below.

So she can say but women got pregnant!, ok where are the Polish Jews, any bit of denier trivia she brings up, you can respond ok well where are the Polish Jews . If the holocaust is fake 3 million people who formed a dynamic part of Polish society should be easy to find. But we cannot because sadly they like so many others were murdered.

In general holocaust deniers have a hyper specific focus on the camps and pop knowledge about the holocaust. Expanding the discussion to the wider war in the east can expose how built on straw they are.

You can ask her where the traditional narrative breaks down for her?

​

Does she deny that Germany started an aggressive war in the East intending to create an Eastern Empire for "living space"

Does she deny that this Empire was to be built on the destruction of Slavic civilization and the wholesale slaughter of certain peoples as proposed in General plan Ost?

Does deny Hitler intended to destroy Slavic art and culture?

Does she deny the wholesale murder of the Polish intelligentsia?

Does she deny deny the existence of the Commissar order?

Does she deny that Soviet POWs were systematically starved by placing thousands in "camps" without food or shelter?

​

I don't recomend you barrage her with these questions but rather explore what the war in the east was with her. There are plenty of videos of Hitler and Nazi officials oppenly stating most of these, and exploring the Eastern Front is not something deniers usually do they want to argue about minutiae about gas chambers and pregnancy. I think once you understand how brutal the Eastern Front was it's a lot easier to accept the holocaust. And remember there as still the missing Polish Jews, you could disprove the existence of the camps all together and there would still be a giant hole where the Polish Jews should be.

Citations: Witold Gadomski, Spłata długu po II RP. Liberte.pl

"Jews in Poland Since 1939" (PDF) Archived November 7, 2006, at the Wayback Machine., YIVO Institute for Jewish Research, The YIVO Encyclopedia of Jews in Eastern Europe, Yale University Press, 2005

Druckman, Yaron (21 January 2013). "CBS: 27% of Israelis struggle with Hebrew". Ynet News. Retrieved 15 December 2017.

http://www.prb.org/Publications/Articles/2014/israel-demography.aspx

/u/estherke has previously written about pregnant women in Auschwitz

See also How common was sexual violence against women (or men) during the Holocaust? answered by /u/commiespaceinvader which explains why some prisoners became pregnant, though others were deported to the camps while pregnant. There is another thread where he explains the differences between Aktion Reinhard camps and other death camps

/u/kieslowskifan has previously explained the difference between concentration camps and death camps, but some camps (like Auschwitz and Majdanek) were both.

There is a specific section of the subreddit FAQ about Holocaust denial

EDIT: removed 4th ping, which was not specific enough.