Amos, first of all, I must say I have much esteem for Bnei Noach like yourself who see the Torah as the universal law for all mankind. Blessings for success in all!
Now in regards to your questions, within the first 40 days from conception the fertilized egg is considered mere water only in regards to being liable in a court to capital punishment. Nevertheless, an abortion during those 40 days is nevertheless forbidden under the prohibition of murder. There are two exceptions to this according to some Poskim where the Halacha is more stringent for Bnei Noach than for Jews:
In regards to the case you mentioned where the child would end up having serious malformations that would impede it from living a normal life, Rabbi Moshe Feinstein permits an abortion only within the 40 days, however an Halachic Authority should be consulted on a case-to-case basis due to the severity of the prohibition. The only other exceptions are when there is a strong emotional reason for a mother to abort like rape or incest within the 40 days (the law in this case is more stringent in regards to Gentiles but Rabbi Moshe Feinstein is lenient under dire circumstances) or a case where the baby is threatening the mother’s life even after the 40 days before the baby’s head emerges.
I suggest you buy The Divine Code, you can get it on Amazon Kindle if you like.
I recommend reading the source of what I wrote, especially in light of the severity of the prohibition of murder:
Excerpt from The Divine Code
By Rabbi Moshe Weiner
Details of the Prohibition of Murder
- One who hits a pregnant woman and kills her fetus, or a doctor who performs an abortion by which the fetus cannot possibly live, or a doctor who gives the mother medicine for the purpose of aborting the fetus or killing it in place, or a pregnant woman who did this herself, are all liable to be punished for murder in a court of law. However, one who hits a woman in another area of her body, which causes her to weaken and subsequently miscarry, is not liable in court unless he has intention with his action to cause the miscarriage, and the miscarriage was inevitably a result of the blow (see topic 5:7 below). One who hires a doctor to perform an abortion is considered as one who hires a mercenary to kill, and this is punishable by God.
- An implanted embryo is not judged to be a human life until 40 days after conception. Until then, its substance is considered like mere water, but during that time, it is still forbidden within the prohibition of murder to cause an abortion, and God will seek justice for the destruction of the implanted embryo. Nevertheless, within 40 days after the egg is fertilized (the moment of conception), a killer of an implanted embryo is not liable to capital punishment by a court of law.
- Even if the mother has emotional justification for not wanting the pregnancy (for example, in cases of rape or incest), aborting the fetus is forbidden according to the severity of the prohibition of murder. If it is known that the child she is carrying will be born with a fatal illness or defect, it is nevertheless forbidden to abort the fetus, and one who does so is a murderer. It would appear that if it is medically proven that the fetus will be miscarried or not born alive, or that it will be born but will die within 30 days, then one who transgresses and aborts such a fetus is not liable to capital punishment from a court of law.
- A pregnant woman whose own life is at risk because of her pregnancy is permitted to have an abortion (see topic 3:7 below). The use of methods that prevent conception from happening is permissible for Gentiles, as explained below in Chapter 9.
- One who kills a born child that could not have lived for 30 days after birth, due to a serious illness or defect, is exempt from liability to capital punishment. If, however, the child could live at least 30 days after birth, even if only through medical intervention, it is considered viable, and one who kills it is liable to capital punishment.
Laws of a Pursuer and Self Defense; Saving the Life of a Woman in Danger from Childbirth
- If a woman is at risk of dying in childbirth (due to her fetus), it is permitted to kill the unborn fetus and remove it from her to save her life, because it is as if the fetus is pursuing her to kill her. But if its head has already emerged, since it is already born, it is forbidden to harm it, for one does not have permission to choose one life over the other, and this risk in childbirth is the nature of the world. If taking no action against the fetus would result in both the mother and the fetus dying, or if it is clear that the child will be nonviable no matter what, or it will be stillborn, it is permissible – if necessary to save the mother’s life – to kill the fetus, or the nonviable child even if the head or most of the body has come out.,1044
 Rashi on Tractate Sanhedrin 57b.  If the aborted fetus might survive in an incubator, but the doctor does not intend this, and it isn’t done, this is considered murder; see topic 4 above.  Since the abortion-inducing medicine will surely take effect in her body, it is tantamount to the case where one pushes a victim into a pit where he will surely die from hunger or lack of air, and this is direct murder for a Gentile. Although Rambam, Laws of Murderers ch. 6, differentiates between a murder caused directly from one’s own power or that comes as a result of one’s actions, this difference applies only for inadvertent killing by a Jew.  See Kli Ĥemda Parshat Shemot, paragraph 4, which holds that even though a Gentile who hires others to kill is liable to be punished by God, this only applies if the victim is a born person and not a fetus; in the author’s opinion, this reasoning does not appear to be valid.  Tractate Bechorot 47b; Shulĥan Aruĥ Yoreh De’ah 305:23.  In this case, as for any murder, the blood of the victim and of the would-be descendants are all avenged, as God said to Cain (Gen. 4:10): “The voice of your brother’s bloods, they cry out to Me…” Based on Sanhedrin 37a, Rashi explains this as “his blood and the blood of his [would-be] descendants.”  Responsa of Beit Shlomo Ĥoshen Mishpat ch. 132; Aĥiezer 3:65; Ĥemdat Yisrael Hilĥot Melaĥim 9:7. (In medical terminology, the transition from an implanted embryo to a fetus is complete at the ninth week after conception.)  See Responsa of Ĥavot Yair ch. 31, who gives no permission for abortion even in the first 40 days, even for an embryo conceived out of wedlock; Tzitz Eliezer vol. 9, ch. 51, permits this for a Jew. Igrot Moshe Ĥoshen Mishpat vol. 2, 69:3, states that for a Gentile this is permitted in a dire case.  Igrot Moshe Ĥoshen Mishpat vol.2, ch. 69 and 71. Sridei Aish vol. 1, ch. 162, permits abortion for a Jew in the first 40 days if the child will have a permanent illness or defect that will impede normal living; it appears that the same applies for Gentiles and there is allowance for them to do so, but requests for this permission should be judged very carefully because of the severity of the prohibition of murder if it is done without correct justification.  This is based on the case described in topic 14, when it is medically determined in accordance with Torah-law standards that a born child would have been a short-lived and nonviable. Liability to capital punishment for the transgression of abortion of a fetus applies if it has no defect that would preclude the child from being capable of living for at least 30 days after a full-term birth. See Responsa of Radvaz vol. 2, ch. 695, in regard to Jews.  This is the ruling of Rambam, Laws of Murderers 2:6 regarding a Jew, and Minĥat Ĥinuĥ Commandment 34 and Maharam Shik Oraĥ Ĥayim ch. 142 write that the same applies to a Gentile. (Nevertheless, it is still forbidden to do so, within the prohibition of murder.) The difference between a nonviable child and a mortally wounded living person (for whose murder one would be liable to capital punishment) is that the mortally wounded person has already gained the distinction of viable living, as opposed to a newborn child that emerged so unhealthy that it cannot gain the distinction of viable living. (The ruling is unclear for a fetus that will be born prematurely and then placed in an incubator – especially when there is a good chance that it will fully develop – as to whether a Gentile who aborts this fetus is liable to capital punishment. On one hand, this fetus should be considered as living, since it has a better chance for survival after its premature birth than a mortally wounded person. Conversely, an underdeveloped fetus that will be born prematurely does not yet have the potential to be born as a “viable living person.” The ruling is likewise unclear regarding a woman who died with a 9-month old fetus in her womb: is one who destroys this fetus liable to capital punishment, since it is possible for the fetus to be pulled out alive from the mother? Or is he exempt from capital punishment, since it would die if it is left alone? It appears that in both cases, one who aborts the fetus is exempt from capital punishment because it will not be born as a viable living person, as can be seen from the Responsa of Radvaz vol. 2, ch. 695.)  *Intact dilatation and extraction (“D & X,” commonly referred to as “partial-birth abortion”) of a fetus would not be permitted unless it is the only way medically available to save the mother. In 1996, a select panel convened by the American College of Obstetrics and Gynecologists found no circumstances when this is the only available option for saving the mother. (This document is available on http://mrc.org.) If it is possible to save the mother without killing the fetus, and yet the fetus was killed from the outset, it is considered a case of murder.  *In Torah Law, a child has been born when its forehead, or the majority of its body, has emerged from the birth canal (Shulĥan Aruĥ Ĥoshen Mishpat 287, Shulĥan Aruĥ Yoreh De’ah 14).  Rambam, Laws of Murderers 1:9.  Tiferet Yisrael Bo’az, Tractate Ohalot, end of ch. 7. This law is comparable to the case in which murderers singled out their victim from a group, and will either kill that one victim or the whole group. It is permissible to hand over the one victim, since it cannot be said that the victim’s blood “is more red” than that of the whole group (see topic 2:8, and last footnote to topic 2:4 above).  Panim Meirot vol. 3 ch. 8, and Tiferet Yisrael ibid., and the Mishnah Aĥarona Tractate Ohalot there. Although they write about a Jew, it appears that the same law would apply to Gentiles. See Igrot Moshe Ĥoshen Mishpat vol. 2, 69:2, who explains that unless the head of the child has emerged, it cannot be considered to be as alive as the mother. This logic would apply here, if it is known that after the head emerges, the child will be non-viable. Rabbi Zalman Nehemiah Goldberg notes that it appears that if a child will be stillborn, this is correct. If it is not stillborn, but it will die in any case (as a result of the birth process), it is still a completely live person (even if it is medically equivalent to a mortally wounded person). He thus brings the following question. If the danger from the labor is a “natural process by the Hand of Heaven,” in which either the child or the mother would die, but not both, then the child would not be classed as a pursuer. Then it is not clear that it should be treated differently than the law of a mortally wounded person, in which case a Gentile would be liable for murder if he kills it. So in this case, would it be forbidden to kill the emerging child to save the mother’s life, even though taking no action will otherwise cause the death of both? The author responds that the Talmud, in Tractate Sanhedrin 72b, only instructs no intervention in a case of a natural process in which one of them will live and the other will die (as for example, in Gen. 35:16-20, when Rachel died giving birth to Benjamin, after most of the child’s body had already emerged). But if the child will be non-viable no matter what, at least the mother should be saved, even by killing the child if that is the only way.  See topic 7, in which a woman’s life is being threatened by her childbirth. See Tractate Sanhedrin 72b, that if the head of the child or most of the body has come out, one may not harm it, since it is a natural process that is threatening the mother’s life. However, this rule does not apply if both the mother and the child are “pursuing” each other. In the Jerusalem Talmud, Tractate Sanhedrin, end of ch. 8, the reason given for the prohibition of killing the child after its head has emerged is only due to the fact that we do not know who the pursuer is. However, if it is clear that each is endangering the other’s life, it is permissible to kill the emerging child to save the mother.