"If God had intended that only"
Wow. You KNOW God's mind. Pretty impressive. Can't argue with that.
Me, I have rely on the Bible, the Holy Spirit, teaching of Godly men and women through the years, and my brain.
But since, you KNOW God's mind and intention. You go on your way.
You will find NOTHING in the Bible indicating that intercourse should occur only during periods of peak fertility. OR that we should be concerned about zygote viability at all. Is there a NEW improved version of the Book?
Nor has there been any "teaching of Godly men and women" indicating such things. You have bought this Loon's bogus argument hook line and sinker.
We don't even know what that viability is affected by or how much yet you are willing to call someone a sinner in the face of complete uncertainty. That is fanaticism.