Your Vitamin D level of 21.5 nmol/L is deficient. To safely correct this, you will likely need a high-dose Vitamin D3 (cholecalciferol) supplement. Doctors typically prescribe a 'loading dose' of 20,000 to 50,000 IU once weekly for 6 to 8 weeks, followed by a daily maintenance dose of 800 to 2,000 IU. Since Vitamin D is fat-soluble, take your supplement with a meal containing healthy fats for better absorption. Please consult your doctor for a specific prescription tailored to your health profile, and plan to recheck your blood levels in 3 months.

Severely low Vitamin D during pregnancy can increase the risk of bone weakness, muscle pain, fatigue, and, in some cases, may affect the baby's bone development and birth weight. Taking Cholecalciferol, such as Ultra D3 4K (4000 IU) daily, is often considered safe in pregnancy when prescribed by a doctor, but many women with very low levels may need higher doses or weekly supplements for a short period. It is best to continue the medication as advised and repeat the Vitamin D test after a few weeks to ensure the levels are improving. Also, try to get 15-20 minutes of sunlight exposure and include calcium-rich foods in your diet.