- *There is none. The dragons were lying/mistaken. Evil Bob’s test was inaccurate, or he lied about it. However, When Thomas arrived through the gate, he seemed desperate to ensure that she didn’t go through. He knew she would have a child, and not very long from that time.
- *Ben. Doctor Jacques lied/made a mistake about the procedure Ben requested. When Ben says “our son,” at the end of “Entanglement,” he’s subtly suggesting the future to her semi-conscious brain.
- *Young Thomas. He had the opportunity, and all the motive in the world, at the castle.
- *Older Thomas. In spite of her denial that there wasn’t anything between them during training, the number of marriages she told Cato’s crew doesn’t match the number of marriages we know about. Either they misinterpreted her sleep-talking, or there was another marriage somewhere. Possibly, Thomas insisted on a legal marriage at the start of training. Possibly, he convinced her after her return was so long delayed. On the other hand, if this training was before Thomas met her at the party at his cabin, Thomas is unlikely to have made any romantic overtures to her–after all, he had sworn to himself that he wouldn’t.
- *Evil Bob. He had the opportunity after he rescued them on the sea. He has the technical knowledge and apparatus to have a frozen embryo ready in case the opportunity for implantation would arise, and it did. If he plans to replace his father, he needs his own heir. His later questions to her about the potency of the genetic changes may have been directed to finding out whether her heir would, theoretically, be able to survive to the time Bob needed.
I suspect that, in Master Jackson’s time, the default choice for most women is not to be fertile. Those women who have had this anti-fertility procedure done have access to a treatment (a small, drinkable vial) that causes ovulation and thus temporary fertility. After arranging the kidnapping at Ben’s Paris house and bringing her to the med lab, Thomas was shocked to discover she had no uterus. He instantly ordered that remedied, because he’d seen the observations from the Ireland trip and in those, she was pregnant–that possible future, the one he’d pinned all his hopes on, didn’t exist in a universe where she couldn’t bear a child. She was paying no attention to what was happening to herself as she talked the children through their own healing procedures. Marcel, who obviously knew all about the Ireland trip and the observations, had been watching her medical procedures and had seen what had been done to her. When he tried to draw her attention to it, she turned to look too late.