Who the heck "needs" most any particular exercise? Most of us aren't weightlifting because our jobs or survival against marauding Vikings demands fitness at all, much less specific fitness, but because we pick the goals that suit us.
Deadlifting is great for strength of the entire lower body and lower back, and has the added benefit of teaching your body to work as a linked unit. It's also often liked because lifting such heavy loads causes a release of hormones beneficial to the addition of mass on the body. It's one of the best exercises around.
I do wonder if you could put yourself in danger of having your water break by doing especially hard lower body exercises, though. I suppose you could break your bag doing most anything if the strain is great enough. But then again, you don't need to do powerlifting exercises at max poundage, either. Lighter deadlifts can even be done to great advantage, as when you're using them for controlled negatives. Negatives help build muscle, after all.
For a pregnant woman, this could be an ace in the hole when it comes to silly gym arguments. Pregnant women usually or at least very often have back pain somewhere along the line. Deadlifts, by strengthening the back for the new heavy, unbalanced load of your baby, could protect you from a great deal of discomfort during your pregnancy. Some women even have to take to bed for at least a few weeks of pregnancy because their back pains get too severe. Deadlifts could prevent that. And after your baby is born, you will still be carrying around a lot of extra weight -- plus a baby of ever-growing poundage. That extra lower back strength will come in very handy for literally years, until you no longer carry your baby as much. Heck, I think a lot of women would prefer to carry their babies into their teenage years if they could. So you'll get plenty of mileage out of a strong lower back. Doesn't hurt when you're hauling groceries or bending over to wash the dog, either.
To interject a perhaps borderline crude note prompted by the phrase "bending over," a strong lower back is a visual delight in a woman. John Updike called "the arabesque of the spine" the most beautiful part of a woman. I'm inclined to agree. The transition from the bottom up through the lower back to the rest of the back on a fit, athletic woman is a thing of mesmerizing beauty duplicated nowhere else on the body. And it can stay beautiful well past the time when age has taken a toll on beauty.
So besides the general and functional good deads do and the specific good they might do a woman during pregnancy and after, perhaps the thought that in doing them you are making more beautiful the most beautiful part of your body might strike a chord that motivates you to keep on doing them. Even if, for a while, you make some allowances on poundages so you don't break your water or cause a hemorrhoid or whatever. I know roids are common in pregnancy. (On that last note, be sure to do the "anal lock" -- clench down there -- to help prevent roids when you're lifting.)
Well that paragraph sure went from the sublime to the, uh, earthy.
Anyway, powerlifting movements tend to involve many muscles in the body and are very good for overall health and development. I wouldn't endanger my pregnancy for them, but doing them prudently seems to me like it could actually bring you benefits specific to your pregnancy, not be counter-productive. Maybe that guy you're talking to just hasn't thought things out.