<prompt> Which of the trophoblast does not invade spiral arterioles:-ExtravillousEndovascularTertiary villusInterstitial  <response>: Ans. d InterstitialRef: Williams Obstetrics 25th Ed; Page No-88 After implantation; trophoblast giving rise to villous and extra villous trophoblasts. Extra villous trophoblasts contact with various maternal cell types because it migrate into the decidua and myometrium and also penetrate maternal vasculature. Extra villous trophoblasts are found outside the villus and it is further subdivided into endovascular and interstitial trophoblasts. Interstitial trophoblasts invade the decidua and surround spiral arteries. Endovascular trophoblasts invade and transform spiral arteries during pregnancy to create low-resistance blood flow that is characteristic of the placenta. 