Islam's large corpus of literature allows us to know Muhammad's teachings on a wide variety of topics. From these sources, we learn that Muhammad took it upon himself to teach about human reproduction frequently, and that everything that he taught was completely wrong.
The Quran contains Muhammad's guess as to where semen comes from:
Surah 86:5-7
5 Let people then consider what they were created from!
6 ˹They were˺ created from a spurting fluid,
7 stemming from between the backbone and the ribcage.
There is only one "spurting fluid" which is involved in reproduction, and Muhammad was 100%, verifiably, wrong about where it came from.
Bolstering this, in the Hadith, Allah uses "while you were in the backbone of Adam" (Sahih al-Bukhari 3334) as a euphemism for "before you were born".
Muhammad taught that women have a reproductive "discharge" like unto a man's semen, which was "thin (low viscosity) and yellow":
Sahih Muslim 311
Anas b. Malik reported that Umm Sulaim narrated it that she asked the Messenger of Allah (ﷺ) about a woman who sees in a dream what a man sees (sexual dream). The Messenger of Allah said:
In case a woman sees that, she must take a bath. Umm Sulaim said: I was bashful on account of that and said: Does it happen? Upon this the Messenger of Allah (ﷺ) said: Yes (it does happen), otherwise how can (a child) resemble her? Man's discharge is thick and white and the discharge of woman is thin and yellow; so the resemblance comes from the one whose genes prevail or dominate.
This is also narrated in Sahih al-Bukhari 130, 3328, 6091, and Sahih Muslim 313a, 314b.
Notice the following about the above:
This second point is 100% false. Women do not have wet dreams like men, during which they have a thin and yellow discharge which has genetic material in it. This is indisputably false.
Muhammad was also asked, as a test of his prophethood, what determines whether a child resembles its father or its mother. His answer, which he claimed came directly from God, was that it is based on who "discharges first" during intercourse:
Sahih al-Bukhari 3329
Narrated Anas:
When `Abdullah bin Salam heard the arrival of the Prophet (ﷺ) at Medina, he came to him and said, "I am going to ask you about three things which nobody knows except a prophet: What is the first portent of the Hour? What will be the first meal taken by the people of Paradise? Why does a child resemble its father, and why does it resemble its maternal uncle?"
Allah's Messenger (ﷺ) said, "Gabriel has just now told me of their answers." Abdullah said, "He (i.e. Gabriel), from amongst all the angels, is the enemy of the Jews." Allah's Messenger (ﷺ) said, "The first portent of the Hour will be a fire that will bring together the people from the east to the west; the first meal of the people of Paradise will be Extra-lobe (caudate lobe) of fish-liver. As for the resemblance of the child to its parents: If a man has sexual intercourse with his wife and gets discharge first, the child will resemble the father, and if the woman gets discharge first, the child will resemble her." On that `Abdullah bin Salam said, "I testify that you are the Messenger of Allah."
This is also narrated in Sahih al-Bukhari 3938, 4480.
Again, do women have a discharge, which if discharged before a man's semen during intercourse, will make the child resemble its mother? No, they don't.
A woman does not "discharge" anything during intercourse (or a sexual dream) which has any genetic material in it. A woman's egg is released from her ovaries long before any intercourse could take place in which the egg is fertilized. If what Muhammad says was true, then every child would look like its mother, because the egg is always released before a man's sperm is released. Anyone today can verify that what Muhammad said here, and claimed was from Allah, is 100% false.
In the Quran, carrying on his teaching that only (male and female) semen is involved in the initial creation of a baby, rather than a sperm fertilizing a woman's egg, Muhammad also teaches a cycle of human development in the womb that is utterly absurd, and once again, verifiably false:
Surah 23:12-14
12 And indeed, We created humankind from an extract of clay
13 then placed each ˹human˺ as a sperm-drop in a secure place,
14 then We developed the drop into a clinging clot ˹of blood˺, then developed the clot into a lump ˹of flesh˺, then developed the lump into bones, then clothed the bones with flesh, then We brought it into being as a new creation. So Blessed is Allah, the Best of Creators.
According to Muhammad, a baby is:
Wrong, Muhammad, you lying imbecile. You were 100% wrong about everything that you guessed.
Muhammad repeated his teachings on human development in Surah 22:5, and also prolifically in the Hadith (Sahih al-Bukhari 318, 3208, 6594-95, Sahih Muslim 2643a-b, 2644, 2645a, 2645c, 2646), in which we get timeframes for the respective stages.
For example:
Sahih Muslim 2643a
Abdullah (b. Mas'ud) reported that Allah's Messenger (ﷺ) who is the most truthful (of the human beings) and his being truthful (is a fact) said:
Verily your creation is on this wise. The constituents of one of you are collected for forty days in his mother's womb in the form of blood, after which it becomes a clot of blood in another period of forty days. Then it becomes a lump of flesh, and forty days later Allah sends His angel to it with instructions concerning four things, so the angel writes down his livelihood, his death, his deeds, his fortune and misfortune.
Sahih Muslim 2646
Anas b. Malik reported directly from Allah's Messenger (ﷺ) that he said:
Allah, the Exlated and Glorious, has appointed an angel as the caretaker of the womb, and he would say: My Lord, it is now a drop of semen; my Lord, It is now a clot of blood; my Lord, it has now become a lump of flesh, and when Allah decides to give it a final shape, the angel says: My Lord, would it be male or female or would he be an evil or a good person? What about his livelihood and his age? And it is all written as he is in the womb of his mother.
Above, and in the other referenced passages, Muhammad taught:
In all of his teaching on the development of a baby, Muhammad demonstrated utter ignorance of the fact that a woman had an egg, which was fertilized by a man's semen. Instead, his teaching is centered on the theory that men and women each discharge liquid semen, which mixes together, with one finally prevailing over the other. He also demonstrated total ignorance that a baby in a mother's womb looks like a little human, with a face, neck, torso, arms, and legs, from about 8 weeks on.
Finally, notice that he taught that a baby is predestined to be a "good or evil person", something covered in much detail in this article.
Whenever Muhammad spoke on something which could not be verified back then, but now can be checked, he was found to be wrong. Consider the above passages, and then consider what they imply about his "theological" revelations. If his theological revelations are even half as wrong as the above, Islam is bound to teach scores of blasphemous lies about God and what He wants us to do - which is exactly what we find, when comparing Muhammad's fake revelations with the real Word of God.