I was pretty adamant that DF tell DSD's mom - I didn't want her to hear it from DSD.
It was a little weird. A few months before that, I had thought that I might me pregnant (unplanned). DSD's mom was working with DF at the time, and he mentioned it to her. She broke down crying. Apparently she thought that DF wouldn't have any children other than DSD.
I got the feeling that she wasn't quite over the relationship, which made me suspicious of her motives for a long time. So I was worried about her reaction to the impending birth. But she took it pretty well. She said that she wasn't surprised.
Here are a few things that I experienced that you didn't specifically ask about, but they aren't things that you would know to ask about, kwim? Having a baby with someone who has already had a baby is a strange proposition. I think that it is different when neither of you know what to expect. DF had not only been with DSD's mom, but he had another girlfriend that he met when she was pregnant (she was a rape victim). So he had been present for two births and was around for two infancies.
One of the strange things about being pregnant is that everyone who you meet that has been pregnant will offer advice and relate their stories to you. DSD's mom was no exception. Granted, the woman had given birth four times, so she was experienced in the matter. But I just wasn't in a place where I wanted to hear stories of her pregnancy with DSD.
Before I was in the picture (and even for some time after) DF and DSD's mom's lives were very intertwined. She lived in the house that he owned. She often borrowed money from him. She called him to help her out a lot. I just couldn't deal with that once I became pregnant. The mama bear protect-your-family instincts kicked in. DSD's mom was not DF's responsibility anymore. I felt that he needed to focus on the family that we were building, not DSD's mom's family. We wound up in counseling over this point. Things are different now, but probably in part due to the stink I made when I was pregnant with DS. I felt that DF had to decide where his priority was - our family (including DSD), or DSD's mom's family. At one point I told him that she was only entitled to one emergency favor per month. The fact that he thought (at the time) that this was unreasonable says something.
I remember being afraid that DF would compare me to DSD's mom. She had given birth three times before having DSD, so I figured she was probably experienced and had been a model birther. She had a homebirth with DSD, and DF wanted to use the same midwife. Luckily, she was in school and unavailable. I'm sure she is a good midwife, I just wanted things to be different for us.
Since DSD's mom was an experienced mother before having DSD, I was worried that I would look like an absolute idiot when I had DS. I didn't know how to give birth, I didn't know how to breastfeed. I will probably never forgive myself for this, but I remember being hesitant to try breastfeeding DS right after giving birth because I was afraid that I would do it wrong. And DF would compare me to DSD's mom, who had done it before. Luckily, the midwife that was supposed to attend my homebirth (I had to transfer care a few weeks before my due date for PIH) was my labor support, and she encouraged me to feed DS while we were still in the delivery room. I was able to focus on DS and her instructions and ignore DF.
The weird part about the whole thing was that everyone said that I didn't act like a first time mom. They said I looked like I had already had several babies. DS was having heart decels and I wound up pushing him out in 15 minutes - I didn't have time to think about being nervous or DF's opinion on my birthing style (Or anyone's opinion, for that matter). So I was worrying for nothing.
Then, after we were home, DSD's mom brought DSD and her sister over to meet DS. We have a picture of DSD's mom holding DS with DSD in her lap. It squicks me out completely. Maybe that is wrong, but my post-partum hormonal self wanted to rip my baby out of her arms and beat DF over the head for making me endure a visit with DSD's mom less than 48 hours after giving birth. I wound up telling him my feelings on this many months later. He had no idea how I felt.
One thing that I want to be clear about is that DSD's mom tried to be very nice to me while I was pregnant. When she picked up DSD when I went into labor, she brought me tea. She wanted us to have a lot of things from DSD's babyhood, which was another thing that I just could not deal with. I wanted my own baby things. It was nice of her to offer, but I wanted my own nursing pillow, ykwim? I didn't want DF reliving DSD's babyhood surrounded by the same things with a different partner. Luckily, we moved a few times while I was pregnant, and pretty much everything that DSD''s mom bestowed on us (I said "no" to most everything, but a few things slipped through) was "lost in the move."
Well. This is WAY longer than I intended it to be. Once I started typing, It all seemed to come back.