 Why didn't the Lieutenant know she was pregnant?
SPATIAL DELIVERY BY RANDALL GARRETT Women on space station assignments shouldn't get pregnant. There, high in the emptiness of space, Space Station One swung in its orbit. Once every two hours, the artificial satellite looped completely around the planet, watching what went on below. Outside its bright steel hull was the silence of the interplanetary vacuum; inside, in the hospital ward, Lieutenant Alice Britton clutched at the sheets of her bed in pain, then relaxed as it faded away. We're over Eastern Europe now, but as soon as we get within radio range of New Mexico, I'll beam a call in." Your husband may be the finest rocket jockey in the Space Service, but that doesn't give him the right to come blasting up here on a supply rocket just to get you pregnant!" "But that was two and a half months ago! "Lieutenant Britton, it is my personal opinion that you need your head examined, and not by a general practitioner, either! The terrible pressure of a rocket landing would increase her effective body weight to nearly half a ton; an adult human being couldn't take that sort of punishment for long, much less the tiny life that was growing within her. According to the major, the baby was due sometime around the first of September. And then, only half an hour ago, a meteor had hit the radar room. The depressurization hadn't hurt her too much, but the shock had been enough to start labor. But as soon as we get within radio range of White Sands, I'll ask them to send up an emergency rocket with an incubator. It will be at least three hours before they can get a ship up here. Major Banes was in the Communications Center a full five minutes before the coastline of California appeared on the curved horizon of the globe beneath them. He had spent the hour typing out a complete report of what had happened to Alice Britton and a list of what he needed. When the receiver teletype began clacking softly, he leaned over the page, waiting anxiously for every word. HRS URGENT TO: MAJ PETER BANES (MC) 0-266118 SS-1 MEDICAL OFFICER FROM: GEN DAVID BARRETT 0-199515 COMMANDING WSRB ROCKET. Each room of the space station was protected by airtight doors and individual heating units; if some accident, such as a really large meteor hit, should release the air from one room, nearby rooms would be safe. Banes' next stop was the hospital ward.
 She has an irregular cycle.
 She has an irregular cycle.  She had her tubes tied before going into space.  She wasn't keeping track of her cycle.  Women don't have periods in space.