Limited data exist regarding the course of abnormally invasive placentation (AIP) (=placenta accreta spectrum (PAS)) during the 2nd and 3rd trimester, although this knowledge would be important for optimal patient care. In this retrospective single-center longitudinal cohort study, potential aggravation of AIP was evaluated in 37 patients with ultrasound (US) pictures stored on a minimum of two visits. Five raters, blinded to diagnosis and gestational age, judged the degree of AIP as recommended by the International Society for PAS. The probability of invasiveness was estimated as absent, low, intermediate, severe (0–3 points), the extent as absent, focal, diffuse (0–2 points), and the presence and appearance of each US-sign as absent, mild, severe (0–3 points). None of the 10 judged signs appeared more severe (p ≥ 0.41) with progressing pregnancy. Neither the number of positively scored US-signs (earlier scan; 6.14 ± 2.06, later scan; 5.94 ± 2.16; p = 0.28), nor the estimated probability & extent of AIP rose (3.69 ± 1.15 vs. 3.67 ± 1.22; p = 1.0). Test-retest reliability corroborated excellent agreement between visits (mean number of positive US-signs ICC (3,1) = 0.94, 95% CI 0.91–0.97; p < 0.0001). Overall, there was no clinically detectable increase in invasiveness over the course of the 2nd and 3rd trimester. This should be further evaluated in prospective studies.