“I never gave much thought to DNA,” Sara Lamm intones at the start of “Thank You for Coming,” a position that she had to change upon learning at 29 that the man she called “Dad” wasn’t her biological father. This isn’t to say she hadn’t been thinking about parentage a lot – not only a mother herself, she was engaged on another project, “Birth Story,” which she co-directed with Mary Wigmore about Ina May Gaskin who popularized midwifery among a new generation during the 1970s. Yet when it came to her own birth, things got considerably more complicated, a journey that she documents in compelling fashion in her third feature.

Having once been a performance artist who drew heavily from her personal experience for her work in college, Lamm not only lays herself bare for “Thank You for Coming,” but does so artfully, offering wry commentary to accompany her search for her biological father, an adventure that takes her from Hawaii to North Carolina with many stops in between. Finding a collaborator of sorts — and potential sister — in Jennifer, a vivacious brunette in Maui with whom she shares a similar build, she traces her roots back to a medical school where it was standard practice during the 1970s to mix sperm samples, all the while circling back to the man who raised her, whose admission of how she was conceived came as he discovered he had cancer. While connecting the dots of who the donor was that provided half of her DNA provides much of the intrigue, Lamm’s many detours into exploring what it actually means to become a family, exploring the relationship between her parents who divorced when she was two and forging a sisterly bond with Jennifer regardless of the result of their DNA test, are equally rich.

On the eve of the film’s premiere at the Los Angeles Film Festival, Lamm spoke about what it was like to do such a deep dive into her own history for all to see, literally finding the right tone in her voice to tell the story and how the personal can become universal.

How did this come about?

I had known I was donor-conceived for a long time and I had dipped in and out of working on a film about it, but then I got distracted and worked on my second film, that I co-directed with my friend Mary called “Birth Story.” Basically, life kept getting in the way and at the same time, technology was changing, so I actually couldn’t have made the film I ended up making even five years prior because the genetic testing companies didn’t exist and certainly they didn’t have the databases that they [now] have. It wasn’t until I connected with this woman Jennifer, who was much more immersed in the world of genetic geneology than I was, and once it became clear that we were going to take a DNA test together [to see if she was my sister], that’s when I made the promise to myself I was going to go on this journey and I was going to set the camera up and document everything that happened.

It would seem intimidating enough to ask others, even in your own life, about such a sensitive subject, but was bringing a camera into it an additional challenge?

You’re right, that bringing a camera into a situation is a delicate thing, and I was very aware of how that could change the dynamic. But I also have had enough experience with it to start to develop a confidence that when you introduce the camera, you begin to bear witness in a different way and that there is usually a positive outcome. I committed to showing up with the camera to film whatever it was that occurred with the understanding that probably something beneficial would come about, though I may not have known what the benefit would be. [laughs]

With Jennifer in Hawaii, you in California and your birthplace being in North Carolina, this is taking you to very different parts of the country. Were there cultural differences in the attitudes towards the subjects of conception and family?

I think of it as a North Carolina film, even though it only takes place in North Carolina for a short period of time because the people that I was connecting with were tied to that place for the most part and we were all united in having been there at a particular time, so I wouldn’t say that I encountered a lot of different ideas of family, although in the research I did outside of the film, there was much more breadth and experience. For example, I did some research on single mothers by choice, and families of same-sex parents and they have a very different kind of situation, especially people who have come through the fertility industry later – they have a different relationship to it because the attitudes have changed. The idea that you shouldn’t tell people [about being conceived through a sperm donor] has changed as well and that really shifts the experience of the offspring.

Was this always going to be fairly exclusive to your experience or did you ever envision this as something larger?

Having made a film in the past that was about birth, which is such a big topic, and really diving into the experience of a particular community and spending a lot of time thinking about the larger implications, I really made a choice with this film to pull back and focus on one story of my own relationship to this material. What was great is that through meeting Jennifer, I was able to explore someone else’s story at the same time because it took some of the emphasis on my story and helped to broaden it out. a little bit more. With that being said, I’ve met with a number of donor offspring who were conceived in the ‘70s and many of them share the same details, like the mixing of sperm [in the samples given to prospective mothers] and looking in the medical school class photographs [for potential donors who share physical similarities] – so I’m hoping that it might feel good to donor offspring who might’ve had similar stories to see them themselves reflected. But at some point, I had gone out and interviewed a couple other donor-conceived people and it just felt like this wasn’t the kind of film where we were going to get a whole lot of other different perspectives. And I had my hands full telling my own story.

At what point do you write the narration for this? Much of the wry tone and most personal observations come from there.

Once I got into it, I really enjoyed the writing of it, but it was the biggest challenge. In fact, my editor Susan Metzger and I made a decision to edit the film to get as far along as we could without narration, and when I wrote the narration, I would write it and record it into my iPhone and AirDrop it to her as she was sitting right next to me and we would tweak it based on how it would work. But we didn’t start playing with the narration until the film was about 80 percent cut, so the structure of the film was pretty much what it looks like now and we had marked in our heads,”Oh, this might be the way to transition,” but once I started writing, it would affect the work that we would cut. I had never written narration before and I wasn’t quite sure how you would wed words to images in that way because it should feel in retrospect like they were always together. I didn’t quite know, but that was how we did it.

At one point, you introduce footage that your father shot of your mother that you get from a relative. Did you know what kind of film you might have to work with from the past before making this or did this film prompt that kind of discovery?

I had no idea that that footage existed. I knew that main footage of me with my mom existed because I had that for a long time and that came from a different source. Some of the other archival came from my uncle, who gave it to me because I think he knew that as a documentary filmmaker, it would probably be safe and I would know what to do with it. I’d expressed an interest in stuff that he had shot over the years, so it was a combination of those two different bits of archival resources that really made all the difference. When you start working on a project like this, I find that there is often some synchronicity and that arrival of the footage from my uncle is one of those things that I count as synchronous.

Was the film about something else than you thought it would be when you started?

I think so. It’s very interesting if you think that the search was about a search for my father and to realize that the character to me that comes most alive is the relationship with my nonbiological father – the man I call my Dad, so in searching for my biodad that in some ways I became closer to my non-bio dad. I didn’t expect that.

What’s it been like to be bringing this into the world?

I’ve been working on it for a long time, so I’m excited for people to see it and I’m a little bit nervous because I’ve never made a film this personal before, so nerves are baked into it – I always felt like I could make a film that both felt personal but that hopefully wouldn’t be so personal that it would be overwhelming for me or for the viewer. So I am excited to show it to people, especially friends and family who have been watching me go through this in real time, the finished product.

“Thank You for Coming” does not yet have U.S. distribution. It premieres at the Los Angeles Film Festival on June 18th at 12:45 pm.