hi littleducks ,
Have a really good look at the <a class="break-all" href="//www.vitamindassociation.org" rel="nofollow" target="_blank">www.vitamindassociation.org</a> website. On the front page you will find a lecture by Prof Hollis, Medical University of South Carolina , concerning Vit D , pregnancy and breastfeeding. He is one of the world's foremost experts. You will find many pages of valuable advice and information on that site.
Having found that you are deficient , at an early stage of pregnancy means that you have the opportunity to greatly enhance your health, particularly throughout pregnancy and delivery . You baby's health whilst developing in the womb will be helped, in later life your baby's chances of developing autoimmune diseases are thought to be reduced, your babies chances of developing quite a few other conditions are thought to be reduced. ( Schizophrenia, Diabetes etc etc. )
You will see that Prof. Hollis' protocol is 4000 IU per day , throughout pregnancy. Then, if breast feeding , 6000 IU per day. Your milk will then have a replete level of vitamin d for your infant. That would be approx 400 IU per litre of milk. That level of 400 IU per litre is found in humans , living an outdoor , healthy , ancestral lifestyle. They do not need to supplement their babies with Vit D. Here in the UK , mothers are generally much lower in Vit D, and so their milk contains just 25 IU per litre. For this reason , the government recommends that breast fed babies receive about 300 IU per day. In the USA the recommendation is 400 IU per day , from birth , for breastfed only babies.
Professor Hollis has shown , with several, placebo controlled , randomized trials , that being replete with Vitamin D , your chances of developing pre-eclampsia will half, the chance of needing a ceasarian will roughly halve, your chances of developing bacterial vaginitis will be about half, plus other benefits too..!
You are being treated by your doctor , so it may be best to talk to him about any changes that you might intend to make with the compounds you intend to take. Prescription medicines are very tightly controlled. If you decide to change to "over the counter" preparations , please make sure they are of good quality. If you took 6,000 IU per day, that would be equivalent to your prescription of 20,000 IU @ twice a week.( to a close approximation).
Vitamin D researchers , in general would prefer daily dosing , rather than intermittent bolus dosing. Daily dosing more closely replicates the way humans received their vitamin D throughout their evolution , in sunny Africa. Have a look at the lecture I posted earlier on in this thread. (Prof Veith ,) where this is explained.
Your folic acid is very important as well !! However , there are probably more knowledgeable people on here mumsnet to talk about that etc.
Best of luck with the pregnancy.
BTBH