Just curious if anyone noticed this going from a restricted carb diet to a more restricted carb diet. (I don't mean SAD diet to low carb)

Yes.
I could not conceive without the help of IVF. We tried for 3 years and our 4th IVF before we got pregnant and stayed that way.

This past May, I started Dr. Simeons HCG Diet. Very Low Carb, Very Low calorie. I then went on atkins, but ate mostly protein and fat.

I just found out 2 weeks ago that I am pregnant..on my own. I've been ovulating for a year. I've never done that - I have PCOS.

Very Low Carb definitely helped me. I have no doubt about that.

I find that with any weight loss over 10 pounds my cycle regulates. It took a year of ttc to get pregnant with my first. I am not ttc now as I am single but I still pay attention to what's going on with my body. When eating carbs and gaining my cycles were about 45 or more days. Usually when losing I get around 32 days. Hope it stays this way. I would love to have more children in the future---assuming I meet someone.

Fertility will improve with sufficient vitamin D supplementation/status.

Not just for women either.
Vitamin D also improves men's testosterone levels and on the basis of the marked expression of Vitamin D Receptor and the Vit D metabolizing enzymes in human testis, ejaculatory tract and mature spermatozoa, we suggest that VD is important for spermatogenesis and maturation of human spermatozoa.

Vitamin D receptor found in human sperm That implies it is set up to expect vitamin d available at the point of conception.

I've heard of women who previously infertile fell for unplanned pregnancy on correction of Vitamin D status, combined with weight loss from a low carb diet so if you're not careful you may be gaining weight for unplanned reasons.

I was wondering about that - shouldn't fertility improve when carbs are added? Like the body would gain weight in the spring with extra fruit and other nutritious foods abound preparing the body for pregnancy? (I am not talking about SAD or obese women).

Vitamin D? Really? My DH had been on Vitamin D prescription for about a year or so. He had poor morphology - which is one reason we had to do IVF.

If Vitamin D does help sperm, then wow - this makes even more sense!

I'm lc'ing to try and get pregnant. We've been ttc for 18 months. I'm told even a modest decrease in my weight can help. Also if you have an undiagnosed gluten intolerance that can prevent you from absorbing the proper vitamins to get pregnant. I'm on - wait for it - 4000uis of vitamin d. Seriously! There is research that says it decreases your chances of miscarriage too.

Absolutely positive. That is the amount women need to be sure there needs are met through pregnancy. and while breastfeeding 6400iu/d may be required to ensure breast milk is fully vitamin d replete for the baby. Remember also this work was done at latitude 32n and you may live further north (less sun)

and pre eclampsia and gestational diabetes

Trouble with prescription vitamin d is that it is NOT the human form. Cholecalciferol is not patentable so no one pays to get it licensed for prescription therefore it's only available over the counter. Ergocalciferol, vitamin d2, the prescription form is not converted to D3 in some people, I've heard from people taking 150,000iu/daily/D2 on prescription and still remaining vitamin d insufficient. Changing to D3 usually means people can manage on a third or less compared with prescription D2. 50,000iu/d3 is available online if you search or follow links on The Vitamin D council website.

Do remember if It takes time to top up your vitamin d tank The time to start supplementing with D3 is probably 3 yrs before you want to plan a pregnancy. Obviously better late than never but it's not a magic bullet that works instantly. Sure after a month of D3 circulating levels will rise but that is like saying we've opened have now got water flowing through the irrigation channels. If the land has been suffering drought for the last 30+ years the fact that water is beginning to flow along the irrigation system does not mean that the whole field and all the topsoil is fully rehydrated. It will take time for the desert to become fertile again. In the same way it takes time for every cell in your body to have it's full complement of D3, (magnesium and omega 3)

Three years????eeek! Well this explains to some degree the masses of women I've met at the fertility clinic I go to that are 30 or younger with unexplained infertility (in Canada).

Very interesting topic. I will certainly try vit D experiment.

Probably you can share some other ways to improve fertility as well ?

3 months ago I had laparascopy with ovarian cyst removed and since then TTC without success as of now

So I am somewhat anxious this cyst/surgery could have impaired my fertility status. And looking for the ways to enhance it...

I've been looking into the role of melatonin recently, not just for it's role in obesity/diabetes/Alzheimer's but generally or blood pressure reduction, bladder control, it's one of those pleiotropic substances that affects almost everything else.

Both for male (sperm quality motility) and female fertility (ovulation) melatonin has a role.

More on melatonin here

More about role of melatonin secretion in digestive system

Good point here. Made me recall about night-lighting techniques as a way to stimulate ovulation: sleeping during cycle at pitch dark and with a dim light at a few days before and after your estimated ovulation.

Has anyone practiced this?

I would recommend 50,000k/wk of vitamin D3 for 3 months.

I've now had over 10 clients get pregnant after a few months of vitamin D3 supplementation. Both partners were taking 50k/wk of D3.

Some of them had no plans to get pregnant and some were on birth control when they got pregnant.

I now warn my all my clients before putting them on D3 that they should use a barrier method of birth control if they don't want to become pregnant.