Multivitamin and mineral supplementation prior to conception and throughout pregnancy is recommended by all international guidelines considering pregnancy after BS [14]. The multivitamin supplement should contain at least the following amounts of micronutrients and vitamins: folic acid—0.4–1 mg, iron—45–60 mg (18 mg after adjustable gastric band (AGB)), thiamine—12 mg, vitamin E—15 mg, copper—2 mg, zinc—15 mg, selenium—50 μg, and beta-carotene (vitamin A)—5000 IU [15].

Folic acid supplementation after BS is still being discussed. For pregnant women who remain obese after BS, the recommended daily dose of folic acid before conception and in the first trimester is 4–5 mg. However, it is not recommended for the whole population after BS because folic acid deficiency is less common than vitamin B12, especially in patients after MS, and over-supplementation of folic acid can mask the symptoms of vitamin B12 deficiency despite augmenting neurological defects. Most studies do not show a higher prevalence of folate deficiency in pregnant patients after BS than in the general pregnant population [2]. Mead et al. showed in their study of 113 pregnant women who had had three types of BS that folate serum levels were increased in all patients apart from two who admitted no compliance to recommended supplementation. High folate levels in patients probably result from the received supplementation [16]. Some studies indicate that continuous, adequate supplementation of standard multivitamin supplements of multivitamins specially developed for post-bariatric patients before and throughout pregnancy reduces the rate of observed deficiencies. In 197 pregnancy cases after RYGB, observed at a bariatric expertise center in the Netherlands, iron serum levels remained stable, folate, vitamin D, and vitamin B12 levels increased, and only hemoglobin and calcium levels were reported to have been decreased [17]. Eissa et al. analyzed a group of 245 pregnant women after SG and found an incidence of anemia of 78.8% [18]. Vitamin B12 should be supplemented in all patients after BS, both during the pre-conception period and throughout pregnancy, either as an intramuscular depot injection of 1 mg every 3 months or orally (1 mg daily). The way of supplementation can be chosen according to individual preference and effectiveness [15].

Iron deficiency anemia is defined by hemoglobin levels below 105 g/L and ferritin levels below 30 μg/L. The minimum recommended daily dosage of iron is 45 mg of elemental iron (18 mg after AGB); however, it has to be adjusted according to the patient’s ferritin and hemoglobin levels [10]. If oral supplementation does not result in elevation of ferritin and hemoglobin levels or anemia is refractory, intravenous infusion should be administered. The dose is calculated based on body weight and hemoglobin level; in most cases, 1000 mg is sufficient to treat anemia, and it takes 6 to 8 weeks for the hemoglobin serum levels to normalize [19]. Intravenous iron infusions are not recommended in the first trimester due to a lack of data [20].

The retinol form of vitamin A is teratogenic and, therefore, should be avoided during pregnancy. Vitamin D should be maintained at a level of at least 50 nmol/L (or 75 nmol/L depending on different recommendations), and the serum parathyroid hormone should be within normal limits, with a possible additional supplementation of calcium. Other studies recommend supplementation of calcium in all pregnant patients after BS [14]. There is a basic risk of thiamin deficiency after BS, which can be augmented in patients who suffer from prolonged vomiting after BS, especially if it is aggravated in pregnancy. In case of prolonged vomiting, each patient should be treated for potential thiamine deficiency to prevent irreparable brain damage [6]. Thiamin is involved in the synthesis of myelin, the formation of mitochondrial and synaptic membranes, and the process of fetal neural and brain development [8].

The serum levels of the following parameters should be checked at least once a trimester: full blood count, including hemoglobin, ferritin, transferrin, folate, vitamin B12, vitamin D, calcium, magnesium, phosphate, and parathyroid hormone, followed by vitamin A, prothrombin time, INR, vitamin K1, protein, albumin, and renal and liver function tests. If any deficiencies are found, the intensity of exams should be adjusted for the optimum monitoring [15].

The diet of pregnant women should be planned with a bariatric dietitian and specialistic dietary care should be maintained throughout the pregnancy. The diet should be prepared individually based on the type of BS, TTC, pre-pregnancy body mass index (BMI), gestational weight gain (GWG), physical activity, and individual food preference and tolerance. General rules include small but frequent meals, long chewing, drinking between (not during) meals, and avoiding simple carbohydrates. According to some studies, pregnant patients who have had BS may require an additional 200 kcal per day [21]. GWG is the preferred indicator for the adequacy of calorie intake [19]. Women with a history of BS are often afraid of weight regain during pregnancy, and their daily caloric intake is insufficient; therefore, it is crucial to provide them with specialist dietary and psychological care. The importance of psychological assistance is also important because depressive symptoms in pregnant women after BS affect approximately one-third of patients [22]. Hedderson et al. presented a telephonic nutritional management program for pregnant women after BS. In a group of 1142 participants, there was a lower risk of preterm birth (aRR 0.48, 95% CI 0.35–0.67), preeclampsia or gestational hypertension (aRR 0.43, 95% CI 0.27–0.69 and RR 0.62, 95% CI 0.41–0.93, respectively), and level 2 or 3 neonate NICU admission (aRR 0.61, 95% CI 0.39–0.94 and aRR 0.66, 95% CI 0.45–0.97, respectively [23]. Araki et al. analyzed the effects of personalized nutrition counseling on pregnancy outcomes and found that regular professional dietary appointments were associated with improved nutrient intake and better food quality habits [24]. The recommended protein intake is at least 60 g daily, while the optimum is 1.5 g per kg per day, and in some cases, it needs to be even higher. If the necessary protein intake is not fulfilled by the diet, it has to be supplemented [15]. Protein malnutrition is defined by serum albumin <25 g/L and is more common after MS, although there is a risk of protein malnutrition after both RS and MS [21].