Does the RCC view 'prevention of ovulation' in the same light as 'abortion'?

There are a handful of cases where it is ethically permissible to administer Plan-B contraceptives

1. The woman is not already pregnant from prior, freely-chosen sexual activity.

2. The woman has been sexually assaulted.

3. The woman has not yet ovulated (i.e. has not released an egg from her ovary into the fallopian tube where it could be fertilized by the attacker’s sperm).

4. The morning-after pill can reasonably be expected to prevent her from ovulating.

So, no prevention of ovulation is not seen in the same light as abortion, but you can't prevent ovulation if ovulation has already taken place, all you can do is wait for the secondary effect of plan b (i.e. starve and murder the most innocent of all God's creatures) to take place.

Catholic hospitals are supposed to require an ovulation test (which is not complicated, may-or-may not be accurate, but is the best we can currently do).

If ovulation tests were entirely accurate, it would be a lot easier to get pregnant or avoid pregnancy, but AFAIK, the best methods of Natural Family Planning are sympto-thermal, which requires daily charting of temperature and mucous. So it's pretty clear Catholic Bioethics is even giving a little leeway in the realm of, "we're possibly killing an embryo, but our best guess is, we're just preventing an egg from showing up. "

Reference: https://www.ncbcenter.org/making-sense-of-bioethics-cms/column-029-getting-it-right-the-morning-after

To those who think it's worth it to worry about the meanings of the words Conception and Fertilization. It's pretty clear that the Church is more concerned about 'ensoulment' and the particulars of that she leaves up to God, granting Him the greatest possible leeway means the-point-that-matters-no-matter-what-you-call-it is at or at least in the process of fertilization.

Mr Rees-Mogg is expressing what would be the popularly viewed position of the RCC.

Are they viewed "in the same light"? Morally, they are both viewed as "gravely disordered".

However, they are two distinct things.

There is a small semantic difference in the way "conception" is used in the medical world and in the Church. In the modern medical view, conception occurs when the fertilized egg implants itself in the endometrium. The more traditional, and Catholic view, is that conception occurs at fertilization.

Therefore, from a medical point of view, anything which prevents fertilization or implantation is deemed "contraceptive". Pregnancy only occurs when implantation occurs.

From the Catholic perspective, oral contraceptives - including the "Plan B" morning after pill - are potential abortifacients. I say potential because, if they fail to prevent fertilization, they prevent implantation of a fertilized egg.

WebMD note on how the contraceptive Apri works (this is true of all hormonal contraceptives):

Apri is a combination birth control pill containing female hormones that prevent ovulation (the release of an egg from an ovary). Apri also causes changes in your cervical mucus and uterine lining, making it harder for sperm to reach the uterus and harder for a fertilized egg to attach to the uterus.

AMA document discussing the Plan B pill:

The Plan B pill is a post-coital contraception method which transiently provides a high dose of (1) combined estrogen and progestin or (2) progestin-only to inhibit or delay ovulation--or induce minor changes to the endometrium to inhibit ovum implantation; therefore, it cannot terminate an established pregnancy

St. Jerome (Letter 22) seems to consider them to be equal in gravity:

But others drink potions to ensure sterility and are guilty of murdering a human being not yet conceived. Some, when they learn they are with child through sin, practice abortion by the use of drugs.

Whereas St. John Chrysostom seems to consider contraception more grave than abortion:

Why do you sow where the field is eager to destroy the fruit? Where there are medicines of sterility? Where there is murder before birth? ... Indeed, it is something worse than murder and I do not know what to call it; for she does not kill what is formed but prevents its formation. What then? Do you condemn the gift of God, and fight with His laws?

Chrysostom's point is that contraception is worse than abortion because, while abortion is the destruction of life, contraception acts to deny the possibility of being.