© 2021 Informa UK Limited, trading as Taylor & Francis Group.Purpose: Thyroid hormones and antibodies are known to participate in angiogenesis and invasion and also thyroid hormone receptors are expressed in the placenta. We aimed to evaluate the relationship of serum levels of thyroid-stimulating hormone (TSH), thyroid hormones (TH), and anti-thyroid antibodies with abnormally invasive placenta (AIP). We also aimed to investigate whether they are related with cesarean hysterectomy and massive blood transfusion need in AIP cases. Methods: A total of 88 pregnant patients were enrolled in this prospective case-control study (30 with AIP, 28 with non-adherent placenta previa totalis (PPT) and 30 controls). Serum TSH, thyroid hormone [T3 (triiodothyronine) and T4 (thyroxine)] and thyroid antibodies against thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) levels were studied in maternal serum at initial admission to our Perinatology Unit (at early third trimester). The factors associated with increased risk of AIP, cesarean hysterectomy, massive blood transfusion, and adverse perinatal outcomes were evaluated with multiple logistic regression analysis. Adjusted odds ratios and 95% confidence intervals were also calculated. Results: Serum TSH and TgAb levels were significantly lower in the AIP group than both PPT and control groups (p =.01, p <.001 and p <.001, p <.001 respectively). Decreased serum levels of TSH (<2.16 mIU/L) and TgAb (<2.70 mIU/L) levels and high previous cesarean section rates were found to be independently associated with AIP in pregnant women with PPT (OR: 0.4, 95% CI: 0.1–0.9; p =.04, OR: 0.7, 95%CI: 0.4–1.3, p =.02 and OR: 0.1, 95% CI: 0.1–0.5, p =.01). Decreased serum TSH and TgAb levels were found to be independently associated with an increased rate of cesarean hysterectomy and massive blood transfusion in AIP cases (OR: 3.7, 95% CI: 1.4–9.8; p =.01, OR: 1.8, 95% CI: 1.1–3.1; p =.03 and OR: 2.6, 95% CI: 1.0–6.5; p =.05, OR: 2.2, 95% CI: 1.1–4.1 p =.02). Decreased TSH and TgAb serum levels were also found to be independently associated with adverse perinatal outcomes in AIP cases (OR: 3.4, 95% CI: 1.3–11.0; p =.01 and OR: 1.978, 95% CI: 2–3.6; p =.03). Conclusion: Decreased serum TSH and TgAb levels, and previous history of cesarean section were all found to be significantly associated with AIP in cases with PPT. We suggest that maternal serum TSH and TgAb levels can provide additional contribution to obstetric Doppler ultrasound in the diagnosis of AIP and thus can reduce the risks of unplanned cesarean hysterectomy in cases with PPT.