© 2020 American Medical Association. All rights reserved. Objective This study aimed to determine whether outcomes differed between infants enrolled in the PREMOD2 trial and those otherwise eligible but not enrolled, and whether the use of waiver effected these differences. Study Design The multicenter PREMOD2 (PREmature infants receiving Milking Or Delayed cord clamping) trial was approved for waiver of antenatal consent by six of the nine sites institutional review boards, while three sites exclusively used antenatal consent. Every randomized subject delivered at a site with a waiver of consent was approached for postnatal consent to allow for data collection. Four of those six sites' IRBs required the study team to attempt antenatal consent when possible. Three sites exclusively used antenatal consent. Results Enrolled subjects had higher Apgar scores, less use of positive pressure ventilation, a lower rate of bronchopulmonary dysplasia, and a less frequent occurrence of the combined outcome of severe intraventricular hemorrhage or death. A significantly greater number of infants were enrolled at sites with an option of waiver of consent (66 vs. 26%, risk ratio = 2.54, p < 0.001). At sites with an option of either approaching families before delivery or after delivery with a waiver of antenatal consent, those approached prior to delivery refused consent 40% (range 15-74% across six sites) of the time. Conclusion PREMOD2 trial demonstrated analytical validity limitations because of the variable mix of antenatal consent and waiver of consent. A waiver of antenatal consent for minimal risk interventional trials conducted during the intrapartum period will be more successful in enrolling a representative sample of low and high-risk infants if investigators are able to enroll all eligible subjects. Clinical Trial Registration ClinicalTrials.gov identifier: NCT03019367. Key Points Waiver of consent is when informed consent cannot be obtained prior to delivery. Cord milking is a procedure in which blood is pushed (stripped) two to four times towards the newborn. Delayed clamping means the umbilical cord is not clamped immediately after birth.