Pregnancy SHOULD result in significant weight gain, if it's healthy. So especially if you start at BMI 16, and end the pregnancy still at BMI 16, absolutely not.
Healthy weight gain during pregnancy requires a gain of on average 25-40lbs/11.5-18kg for one child, for 37-55lbs/17-25kg for twins. Note that my mother, who struggled with untreated Atypical Anorexia most of her life, had twins. Which yes, really fucked with her mental space and body forever more.
---
If you struggle to get to or maintain a BMI 16, or have to think about it and plan in order to stay there, that's the easiest way in the world to determine it is not healthy for you personally. It is clinically significantly underweight, and also, you have to try hard to keep it, and consciously put in effort and control everything around you. So it's obvs not natural, and therefore likely very harmful to your health - regardless of all the unhealthy mindset of the people you have around you, whom I would recommend you get away from as much as possible BTW in favor of healthier people - especially since you will need healthy people around your child also, so they don't grow up with such toxic messages. Also, inherently anybody on a proana website, who is worried about maintaining BMI even in the face of a pregnancy which is obviously going to increase BMI significantly, is clearly not in a healthy space.
---
As a side note, many people who mention being very underweight but not having community members who are concerned, have a few reasons that may happen:
1. a lot of anorexics wear a bunch of layers or baggy clothes, which can hide being underweight
2. if you have smaller bone structure, or a body shape that means all your skinnier features are usually under clothes, people may not be aware
3. about 50% of anorexics grow a much higher body fat percentage as a result of the disease, because the constant malnutrition leads to bone and muscle loss, and then fat retention to try to keep you alive - which means even though one may be struggling so much and so ill and feeling absolutely terrible and yes also very underweight, one might also have the same or more body fat percentage/ratio per weight, as when one was at healthy weight. So it might not look outwardly to some people as though there is a medical problem, even though this is critical. Add to this that many anorexics also have bloated stomachs from destroyed GI systems, and bloated from from b/ping, and sadly many also have edema from heart failure. So there is a critical life-threatening problem that NEEDS interventional, but people many not be able to see it well visually, especially if your body is prone to being really tough and healthy so you still have blood circulation and look halfway alive, or if you were sick your whole life and so people are used to seeing you ill and thus desensitized to it. The antidote to this, ironically, is to eat way more of better foods over a period of at least a year or more, while exercising only a reasonable amount - because then the body actually gets way smaller, since muscle takes up less space than fat, even if the weight stays the same or goes up significantly. Sadly, this is the part where one is engaged in much healthier behaviors, but suddenly everyone around might get worried - because the shrinking and fat loss is noticeable, even though the person might actually be eating 2000-4500 cals per day, and really trying harder to live and harm reduce with the ED, or even if they feel mostly recovered and happier. But admittedly, it is really hard for a person with ED to handle weight loss or fat loss of any sort, without going way overboard.
4. unfortunately, people with naturally curvy, or muscular, bodies may not always appear underweight - especially when clothed - to others. This is because there is shape to the form. Likewise, people who retain a full face despite starvation - which is especially common for younger people. And, people who have issues like hypothyroidism or lipodema, which are both fairly common among anorexics.
5. some people are surrounded in their lives by total dicks, who don't actually give a shit how healthy they are - if this is the case, RUN, and do not look back or take a moment to feel guilty - one can build new family, and new friends, I promise!
--
Nobody with an active ED should be planning to get pregnant though. Having a child while in the throes of a life-threatening mental illness that involves active daily self harm and dangerous thoughts, is obviously not a good idea, when at all avoidable. Recovery is critical - if not prior to pregnancy, then certainly at the point that pregnancy is confirmed if it was unplanned. Fetus development is very fragile, but especially in the early months. The toxic behaviors of ED can have lifetime effects on the baby, and I can tell you from experience, growing up with a mother who has an ED and very low self esteem, is extremely toxic and harmful as an experience also - no matter how much they think they can hide it from the kid, kids internalize that stuff. Pregnancy changes the body permanently - so someone with ED history, even if not an active ED, will need plenty of support, and possibly from ED professionals, to handle feelings about body changes during pregnancy, and after.
And there is nothing like modeling confidence, self love, and self compassion and acceptance, for a healthy baby to grow up around! It changes everything in the world about life. <3